Method and apparatus for transmitting reference signal

ABSTRACT

The present invention relates to a wireless communication system, and more specifically, to a method and an apparatus for transmitting an RS (Reference Signal) from a transmission end. The present invention relates to an RS transmission method and an apparatus therefore, comprising the steps of: confirming RS resources which are defined according to each layer; and transmitting the precoded RS for the layers to a receiving end through a multiple antenna, wherein the RS resource includes a 1 st  index for indicating an RS resource pattern group in which the precoded RS is mapped within a resource block and a 2 nd  index for indicating a code resource for multiplexing the precoded RSs within the RS resource pattern group.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is the National Stage filing under 35 U.S.C. 371 ofInternational Application No. PCT/KR2010/002367, filed on Apr. 15, 2010,which claims the benefit of U.S. Provisional Application Ser. Nos.61/233,124, filed on Aug. 11, 2009, 61/223,063, filed on Jul. 6, 2009,61/173,220, filed on Apr. 28, 2009, 61/173,199, filed on Apr. 27, 2009,and 61/169,697, filed on Apr. 15, 2009.

FIELD OF THE INVENTION

The present invention relates to a wireless communication system, andmore particularly to a method and apparatus for transmitting a referencesignal (RS) using multiple antennas.

BACKGROUND ART

A wireless communication system has been widely used to provide variouskinds of communication services such as voice or data services.Generally, a wireless communication system is a multiple access systemthat can communicate with multiple users by sharing available systemresources (bandwidth, transmission (Tx) power, and the like). A varietyof multiple access systems can be used, for example, a Code DivisionMultiple Access (CDMA) system, a Frequency Division Multiple Access(FDMA) system, a Time Division Multiple Access (TDMA) system anOrthogonal Frequency Division Multiple Access (OFDMA) system, a SingleCarrier Frequency-Division Multiple Access (SC-FDMA) system, aMulti-Carrier Frequency Division Multiple Access (MC-FDMA) system, andthe like. In a mobile communication system, a user equipment (UE) mayreceive information from a base station (BS) via a downlink, and maytransmit information to the base station (BS) via an uplink. Theinformation that is transmitted and received to and from the UE includesdata and a variety of control information. A variety of physicalchannels are used according to categories and usages of transmission(Tx) and reception (Rx) information of the UE.

A Multiple Input Multiple Output (MIMO) scheme increases system capacityby simultaneously transmitting multiple data streams (or layers)spatially using two or more transmission/reception (Tx/Rx) antennas in abase station (BS) and a user equipment (UE). The MIMO scheme may includea transmission (Tx) diversity scheme, a spatial multiplexing scheme anda beamforming scheme.

A transmit diversity scheme transmits the same data through multipletransmit (Tx) antennas, such that it can implement reliable datatransmission without receiving channel-related feedback information froma receiver. A beamforming scheme is used to increase a signal tointerference plus noise ratio (SINR) of a receiver by multiplyingweighting values by multiple Tx antennas. In general, since a frequencydivision duplex (FDD) system has independent uplink (UL) and downlink(DL) channels, high reliability channel information is required toobtain a proper beamforming gain and therefore additional feedbackinformation received from the receiver is used.

On the other hand, a spatial multiplexing scheme for a single user andfor multiple users will be described in brief. Spatial multiplexing fora single user is called SM or single user MIMO (SU-MIMO), and assignsseveral antenna resources of a base station (BS) to one UE. The capacityof a MIMO channel increases in proportion to the number of antennas.Meanwhile, spatial multiplexing for multiple users is called spatialdivision multiple access (SDMA) or multi-user (MU)-MIMO and distributesseveral antenna resources or radio space resources of a base station(BS) to a plurality of UEs.

A MIMO scheme includes a single codeword (SCW) method whichsimultaneously transmits N data streams (or N layers) using one channelencoding block and a multiple codeword (MCW) method which transmits Ndata streams using M (where M is equal to or less than N (where M≦N))channel encoding blocks. Each channel encoding block generatesindependent codewords and each codeword is designed to be able toindependently detect errors.

DETAILED DESCRIPTION OF THE INVENTION Technical Problem

An object of the present invention devised to solve the problem lies ona method and apparatus for transmitting a reference signal (RS) in awireless communication system. Another object of the present inventiondevised to solve the problem lies on a method and apparatus fortransmitting a reference signal (RS) in a MIMO system. A further objectof the present invention devised to solve the problem lies on a methodand apparatus for multiplexing and transmitting a reference signal (RS).

It is to be understood that technical objects to be achieved by thepresent invention are not limited to the aforementioned technicalobjects and other technical objects which are not mentioned will beapparent from the following description to the person with an ordinaryskill in the art to which the present invention pertains.

Technical Solution

The object of the present invention can be achieved by providing amethod for transmitting a reference signal (RS) by a transmitter in awireless communication system, the method including: confirming areference signal (RS) resource which is defined according to each layer;and transmitting precoded RSs for the layers to a receiver throughmultiple antennas, using the RS resource, wherein the RS resourceincludes a first index indicating an RS resource pattern group in whichthe precoded RS is mapped within a resource block, and a second indexindicating a code resource for multiplexing the precoded RSs within theRS resource pattern group.

In another aspect of the present invention, a base station (BS) fortransmitting a reference signal (RS) includes a radio frequency (RF)unit configured to transmit/receive an RF signal to/from a userequipment (UE); a memory for storing information transmitted/receivedto/from the user equipment (UE) and parameters needed to operate thebase station (BS); a processor connected to the RF unit and the memoryso as to control the RF unit and the memory. The processor includesconfirming a reference signal (RS) resource which is defined accordingto each layer, and transmitting precoded RSs for the layers to areceiver through multiple antennas, using the RS resource, wherein theRS resource includes a first index indicating an RS resource patterngroup in which the precoded RS is mapped within a resource block, and asecond index indicating a code resource for multiplexing the precodedRSs within the RS resource pattern group.

In another aspect of the present invention, a method for processing areference signal (RS) by a receiver in a wireless communication systemincludes confirming a reference signal (RS) resource which is definedaccording to each layer; receiving precoded RSs for the layers from atransmitter through multiple antennas; and detecting the precoded RSsusing the RS resource, wherein the RS resource includes a first indexindicating an RS resource pattern group in which the precoded RS ismapped within a resource block, and a second index indicating a coderesource for multiplexing the precoded RSs within the RS resourcepattern group.

In yet another aspect of the present invention, a user equipment (UE)for processing a reference signal (RS) includes a radio frequency (RF)unit configured to transmit/receive an RF signal to/from a base station(BS); a memory for storing information transmitted/received to/from theuser equipment (UE) and parameters needed to operate the base station(BS); a processor connected to the RF unit and the memory so as tocontrol the RF unit and the memory. The processor includes confirming areference signal (RS) resource which is defined according to each layer;receiving precoded RSs for the layers from a transmitter throughmultiple antennas; and detecting the precoded RSs using the RS resource,wherein the RS resource includes a first index indicating an RS resourcepattern group in which the precoded RS is mapped within a resourceblock, and a second index indicating a code resource for multiplexingthe precoded RSs within the RS resource pattern group.

Each RS resource pattern group may be defined in two contiguousorthogonal frequency division multiplexing (OFDM) symbols located ateach slot of the resource block according to an FDM (frequency divisionmultiplexing) scheme, and each RS resource pattern group may include aplurality of resource element pairs temporally contiguous to each other.

The resource pattern indicated by the first index may be represented bythe following table:

TABLE Slot 0 Slot 1 l = 5 L = 6 l = 5 l = 6 k = 11 G0 G0 G0 G0 k = 10 G1G1 G1 G1 k = 6 G0 G0 G0 G0 k = 5 G1 G1 G1 G1 k = 1 G0 G0 G0 G0 k = 0 G1G1 G1 G1

In Table, the resource block includes (12 subcarriers×14 OFDM symbols),l is an integer of 0 or higher indicating an OFDM symbol index, k is aninteger of 0 or higher indicating a subcarrier index, a slot includes 7OFDM symbols, G0 indicates RS resource pattern group #0, and G1indicates RS resource pattern group #1.

The second index may indicate a code resource used as a cover sequencefor the precoded RS in a time domain.

The mapping relationship between the RS resource and a layer index orassociated value may be based on a 1^(st) index first scheme.

The mapping relationship between the RS resource and a layer index orassociated value may be based on a 1^(st) index first scheme when a rankvalue is less than a specific value, and may be based on a 2^(nd) indexfirst scheme when the rank value is equal to or higher than the specificvalue.

The RS may include a dedicated reference signal (DRS), and a mappingrelationship between a DRS resource and a layer index may be representedby the following table:

TABLE [Proposal #1.1-G] Layer DRS pattern Code resource Code resourceindex group index index (opt. 1) index (opt. 2) 0 0 0 0 1 0 1 1 2 1 2 03 1 3 1 4 0 4 2 5 1 5 2 6 0 6 3 7 1 7 3

In Table, the layer index is reordered.

For example, although the entire technology of the present invention hasdisclosed the mapping relationship of resources basically defined as aDRS pattern group and code of a layer, the scope or spirit of thepresent invention is not limited thereto. In another example, theinventive technology of the present invention can also be applied to themapping relationship of resources defined as a DRS pattern group andcode index of a virtual antenna port or RS port instead of the layer asnecessary. In the latter example, a layer and a layer index to bedescribed in the following embodiments may be converted into a virtualantenna port or RS port and a virtual antenna port index or RS portindex, respectively.

Effects of the Invention

As apparent from the above description, exemplary embodiments of thepresent invention have the following effects. The exemplary embodimentscan effectively transmit a reference signal (RS) in a wirelesscommunication system. In addition, the exemplary embodiments caneffectively multiplex/transmit a reference signal (RS).

It will be appreciated by persons skilled in the art that the effectsthat can be achieved with the present invention are not limited to whathas been particularly described hereinabove and other advantages of thepresent invention will be more clearly understood from the followingdetailed description taken in conjunction with the accompanyingdrawings.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are included to provide a furtherunderstanding of the invention, illustrate embodiments of the inventionand together with the description serve to explain the principle of theinvention. In the drawings:

FIG. 1 exemplarily shows a radio frame structure for use in a 3rdGeneration Partnership Project Long Term Evolution (3GPP LTE) system;

FIG. 2 exemplarily shows a resource grid of a downlink (DL) slot;

FIG. 3 exemplarily shows a reference signal (RS) pattern defined in theLTE system;

FIG. 4 exemplarily shows an RS pattern group according to one embodimentof the present invention;

FIGS. 5 and 6 are a conceptual diagram illustrating a method formultiplexing an RS signal in an RS pattern group according to oneembodiment of the present invention;

FIG. 7 exemplarily shows RS transmission channels according to oneembodiment of the present invention;

FIG. 8 exemplarily shows the mapping relationship between an RS resourceand a layer index according to one embodiment of the present invention;

FIG. 9 is a block diagram illustrating a transmitter according to oneembodiment of the present invention;

FIGS. 10, 11, 12, 13 and 14 exemplarily show the mapping relationshipbetween a codeword and a layer according to one embodiment of thepresent invention;

FIG. 15 is a block diagram illustrating a receiver according to oneembodiment of the present invention; and

FIG. 16 is a block diagram illustrating a base station (BS) and a userequipment (UE) according to one embodiment of the present invention.

BEST MODE FOR CARRYING OUT THE INVENTION

Reference will now be made in detail to the preferred embodiments of thepresent invention with reference to the accompanying drawings. Thedetailed description, which will be given below with reference to theaccompanying drawings, is intended to explain exemplary embodiments ofthe present invention, rather than to show the only embodiments that canbe implemented according to the invention. The following embodiments ofthe present invention can be applied to a variety of wireless accesstechnologies, for example, CDMA, FDMA, TDMA, OFDMA, SC-FDMA, MC-FDMA,and the like. CDMA can be implemented by wireless communicationtechnologies, such as Universal Terrestrial Radio Access (UTRA) orCDMA2000. TDMA can be implemented by wireless communicationtechnologies, for example, a Global System for Mobile communications(GSM), a General Packet Radio Service (GPRS), an Enhanced Data rates forGSM Evolution (EDGE), etc. OFDMA can be implemented by wirelesscommunication technologies, for example, IEEE 802.11 (Wi-Fi), IEEE802.16 (WiMAX), IEEE 802.20, E-UTRA (Evolved UTRA), and the like. UTRAis a part of a Universal Mobile Telecommunications System (UMTS). 3rdGeneration Partnership Project (3GPP) Long Term Evolution (LTE) is apart of an Evolved UMTS (E-UMTS) that uses an E-UTRA. The LTE-Advanced(LTE-A) is an evolved version of 3GPP LTE.

Although the following embodiments of the present invention willhereinafter describe inventive technical characteristics on the basis ofthe 3GPP system, it should be noted that the following embodiments willbe disclosed only for illustrative purposes and the scope and spirit ofthe present invention are not limited thereto.

Although the following embodiments of the present invention are focusedupon the LTE-A system, the conceptual reference signal design or variousschemes proposed by the present invention, and associated embodimentsmay also be applied to other OFDM-based systems.

Although the reference signal patterns proposed by the present inventionare focused upon a MIMO condition in which 8 Tx antennas are used in adownlink of the LTE-A system, the proposed RS patterns may be applied tobeamforming or downlink (DL) coordinated multiple point (CoMP)transmission, and may also be applied to the above-mentioned ULtransmission.

For convenience of description, although the exemplary embodiments ofthe present invention are focused upon a Dedicated Reference Signal(DRS), a Demodulation Reference Signal (DM-RS) or a UE-specificReference Signal (UE-specific RS), it should be noted that the exemplaryembodiments may also be easily applied not only to other referencesignals such as a common reference signal (CRS) but also to acell-specific reference signal (CRS) without departing from the scope orspirit of the present invention.

FIG. 1 exemplarily shows a radio frame structure for use in a 3rdGeneration Partnership Project Long Term Evolution (3GPP LTE) system.

Referring to FIG. 1, the radio frame has a length of 10 ms (327200·Ts)and includes 10 subframes of equal size. Each subframe has a length of 1ms and includes two slots. In this case, Ts represents sampling time,and is expressed by ‘Ts=1/(15 kHz×2048)=3.2552×10−8 (about 33 ns)’. Theslot includes a plurality of OFDM symbols in a time domain, and includesa plurality of resource blocks (RBs) in a frequency domain. In the LTEsystem, one resource block includes twelve (12) subcarriers×seven (orsix) OFDM (Orthogonal Frequency Division Multiplexing) symbols. Theaforementioned structure of the radio frame is only exemplary, andvarious modifications can be made to the number of subframes containedin the radio frame or the number of slots contained in each subframe, orthe number of OFDM symbols in each slot.

FIG. 2 exemplarily shows a resource grid of a downlink (DL) slot.

Referring to FIG. 2, a downlink slot includes a plurality of OFDMsymbols in a time domain, and includes a plurality of resource blocks ina frequency domain. Although FIG. 2 illustrates that a downlink slotincludes 7 OFDM symbols and a resource block (RB) includes 12subcarriers, the scope or spirit of the present invention is not limitedthereto and other examples can also be applied to the present invention.For example, the number of OFDM symbols contained in a DL slot may bechanged according to a Cyclic Prefix (CP) length. Each element on aresource grid may be defined as a resource element (RE). One RB mayinclude (12×7 (or 6)) resource elements (REs). The number NDL of RBscontained in a DL slot is dependent upon a downlink transmissionbandwidth established in a cell.

In the LTE system, a Layer 1 (L1)/Layer 2 (L2) control region and a dataregion are multiplexed in Time Division Multiplexing (TDM) in a DLsubframe. The L1/L2 control region occupies the first to third OFDMsymbols of the DL subframe, and the data region occupies the remainingOFDM symbols of the DL subframe. The L1/L2 control region includes aPhysical Downlink Control CHannel (PDCCH) for carrying DL controlinformation and the data region includes a Physical Downlink SharedCHannel (PDSCH) acting as a downlink data channel. To receive a DLsignal, a UE reads DL scheduling information from the PDCCH. Then the UEreceives DL data on the PDSCH based on resource allocation informationindicated by the DL scheduling information. Resources scheduled for theUE (i.e. the PDSCH) are allocated on an RB basis or on an RB groupbasis.

In a wireless communication system, since packets are transmittedthrough a radio channel, a signal may be distorted during transmission.In order to enable a reception side to correctly receive the distortedsignal, distortion of the received signal should be corrected usingchannel information. In order to detect the channel information, amethod of transmitting a signal, of which both the transmission side andthe reception side are aware, and detecting channel information using adistortion degree when the signal is received through a channel ismainly used. The above signal is referred to as a pilot signal or areference signal (RS).

FIG. 3 exemplarily shows a reference signal (RS) pattern defined in theLTE system.

Referring to FIG. 3, the legacy LTE system includes a cell-specific RS(CRS) and a UE-specific RS in a downlink. The cell-specific RS (CRS) istransmitted through all DL subframes. In case of a Multicast BroadcastSingle Frequency Network (MBSFN), CRS is transmitted only through thefirst and second OFDM symbols. CRS is transmitted using at least one ofantenna ports 0 to 3. The UE-specific RS supports single antenna porttransmission of a PDSCH and is transmitted through the antenna port 5.The UE-specific RS is transmitted only when PDSCH transmission relatesto the corresponding antenna port, and is used to demodulate the PDSCH.The UE-specific RS may be transmitted only through a resource blockmapped to the corresponding PDSCH. In FIG. 3, the position of an REmapped to an RS corresponding to the antenna port 0, 3 or 5 is denotedby ‘0’, ‘3’ or ‘5’, respectively. In FIG. 3, ‘l’ is an OFDM symbolindex, and ‘k’ is a subcarrier index.

Antenna port distinction is not physical distinction. A method foractually mapping each logical antenna index or each virtual antennaindex to a physical antenna is implemented in different ways accordingto individual manufacturing companies. The antenna port is not alwaysmatched to the physical antenna on a one to one basis, and one antennaport may correspond to one physical antenna or a combination (i.e., anantenna array) of multiple physical antennas.

The LTE-A system is designed to use a maximum of 8 transmission (Tx)antennas as compared to 4 transmission (Tx) antennas of the LTE system,resulting in an increased throughput. In order to reduce RS overheadgenerated by the increased Tx antennas, a dedicated reference signal(DRS), that may be defined on a UE basis or may be defined on an RBbasis in a frequency domain assigned to a UE, can be used. DRS may beexplicitly defined as a UE-specific demodulation reference signal(DM-RS). The DRS proposed in the present invention may be precoded. Inthis case, as many orthogonal patterns as the number of ranks (layers ortransmission streams) may be used. Needless to say, the DRS proposed bythe present invention may not be precoded. For convenience ofdescription, the precoded DRS and the layer reference signal (RS) may beused interchangeably.

The reference signal (RS) of LTE antenna port 5 shown in FIG. 3 may beused as a dedicated reference signal (DRS), such that backward andforward compatibility with the LTE system can be supported, efforts onthe standard can be minimized, a common reference signal (RS) is definedand reused in various kinds of antenna technologies.

In order to support a maximum rank-8 in the LTE-A system designed to use8 transmission (Tx) antennas, 8 different DRS patterns need to besupported. However, although the precoding scheme may be used on oneantenna port-5 RS patterns or CDM, FDM, TDM or a combination thereof maybe applied to a reference signal (RS) sequence, a sufficient number ofdifferent DRS patterns (e.g., a maximum of 8 DRS patterns) may not bedefined.

In order to solve the above-mentioned problems, another one dedicated RS(DRS) pattern discriminated in time-frequency resources can begenerated. In this case, an RS pattern discriminated in time-frequencyresources may be defined as a separate antenna port.

A reference signal (RS) pattern of the legacy antenna port 5 or anotherRS pattern different from the RS pattern is referred to as DRS patterngroup #0, and still another RS pattern defined to be discriminated intime-frequency resources is referred to as DRS pattern group #1. In caseof the RS pattern of DRS pattern group #1, the same pattern as the RSpattern of the DRS pattern group #0 may be shifted at the level(s) of atransmission symbol and/or a frequency subcarrier (i.e., RE).

FIG. 4 exemplarily shows an RS pattern group according to one embodimentof the present invention.

Referring to FIG. 4, DRS pattern group #0 (G0) and DRS pattern group #1(G1) may be designed in various ways within one resource block (RB).FIG. 4( a) exemplarily shows one DRS pattern group in case of a normalCP, and FIGS. 4( b) to 4(e) exemplarily show four DRS pattern groups incase of the extended CP. Table 1 briefly shows the matrix-format mappingposition of a DRS pattern group in a resource block (RB) including (12subcarriers×7 OFDM symbols) in case of a normal CP (See FIG. 4( a)).Table 2 briefly shows the matrix-format mapping position of a DRSpattern group in a resource block (RB) including (12 subcarriers×6 OFDMsymbols) in case of the extended CP (See FIG. 4( b)). The DRS patterngroups shown in FIGS. 4( c) to 4(e) may be displayed in a matrix formcorresponding to the resource block (RB) as shown in Table 2.

TABLE 1 Slot 0 Slot 1 l = 5 L = 6 l = 5 l = 6 k = 11 G0 G0 G0 G0 k = 10G1 G1 G1 G1 k = 6 G0 G0 G0 G0 k = 5 G1 G1 G1 G1 k = 1 G0 G0 G0 G0 k = 0G1 G1 G1 G1

TABLE 2 Slot 0 Slot 1 l = 4 l = 5 l = 4 l = 5 k = 11 G0 G0 G0 G0 k = 10G1 G1 G1 G1 k = 6 G0 G0 G0 G0 k = 5 G1 G1 G1 G1 k = 1 G0 G0 G0 G0 k = 0G1 G1 G1 G1

In Tables 1 and 2, l is an integer of 0 or more indicating an OFDMsymbol index, and k is an integer of 0 or more indicating a subcarrierindex. In case of a normal CP, the slot includes 7 OFDM symbols. In caseof the extended CP, the slot includes 6 OFDM symbols. G0 is a DRSpattern group #0, and G1 is a DRS pattern group #1. For example, eachDRS pattern group may multiplex a maximum of 4 layer RSs.

In accordance with another embodiment of the extended CP, differentlyfrom FIG. 4( b) illustrating resource elements (REs) each including 12RS transmission subcarriers and Table 2, DRS pattern group #0 and DRSpattern group #1, each of which is comprised of the increased number ofRS transmission subcarriers, may be used to implement more correctchannel estimation under more frequency-selective channel condition. Forexample, each DRS pattern group may be comprised of 16 RS transmissionREs.

Provided that the number of orthogonal DRS patterns to be identified inresponse to an arbitrary rank value or the number (=Rank value) ofvirtual antenna ports to be supported by the LTE-A is set to N (N is aninteger of 1 or higher, for example, 1≦N≦8), M distinctive DRS patterns(where 1≦M≦N) are multiplexed through DRS pattern group #0 (G0), and(N-M) distinctive DRS patterns are multiplexed through DRS pattern group#1 (G1). If there are no distinctive DRS patterns applied to a system inan arbitrary DRS pattern group according to the multiplexed condition,DRS pattern group #0 (G0) is not defined in a resource block (RB) incase of M=0 and DRS pattern group #1 (G1) is not defined in a resourceblock (RB) in case of M=N. In the present invention, a virtual antennaport may be referred to as an antenna RS port in view of an RS. Theantenna RS port may have a logical antenna index or virtual antennaindex of RS resources. In this case, RS resources may be mapped to anantenna RS port of a specific index region.

For example, although the entire technology of the present invention hasdisclosed the mapping relationship of resources basically defined as aDRS pattern group and code of a layer, the scope or spirit of thepresent invention is not limited thereto. In another example, theinventive technology of the present invention can also be applied to themapping relationship of resources defined as a DRS pattern group andcode index of a virtual antenna port or RS port instead of the layer asnecessary. In the latter example, a layer and a layer index to bedescribed in the following embodiments may be converted into a virtualantenna port or RS port and a virtual antenna port index or RS portindex, respectively.

In FIG. 4, it is assumed that each of the number (A) of REs of DRSpattern group #0 and the number (B) of REs of the DRS pattern group #1is set to 12. However, the assumption of FIG. 4 is disclosed only forillustrative purposes. In the present embodiments, although the number(A) of REs contained in DRS pattern group #0 is basically defined to beequal to the number (B) of REs contained in DRS pattern group #1according to the system design purpose, it can be recognized that A mayalso be different from B on the basis of the importance of each layer RSpattern or layer in response to the arbitrary rank value. In addition,as described above, the number of DRS pattern groups, each of which iscomprised of fixed REs based on a specific rank value according totransmission rank setup, may be changed. For example, in case of theentire DRS pattern considering total overhead, if a rank is set to anyvalue of 1˜2, one DRS pattern group is applied to Rank 1 or 2, each RBincludes 12 RS REs. If Rank is set to any value of 3˜8, two DRS patterngroups are applied to the Rank such that a total of 24 RS REs may becontained in each RB.

Each DRS pattern group may be mapped to a separate (virtual) antennaport. For example, if DRS pattern group #0 satisfies an RS pattern ofthe antenna port 5 without any change, the DRS pattern group #0 is setto the antenna port 5, and an RS pattern of the DRS pattern group #1 maybe set to a separate antenna port (e.g., antenna port 6). In addition,definition of antenna ports are departmentalized such that individual RSresources (patterns) pertaining to the RS pattern group may be definedas a separate antenna port. For example, in the case where two RSresources (patterns) are mapped to RS pattern group #0 and two RSresources (patterns) are mapped to RS pattern group #1, four (virtual)antenna ports or RS ports may be respectively mapped and defined.

Hereinafter, the present invention proposes a method for mapping (ormultiplexing) orthogonal or quasi-orthogonal RS patterns of a total of Clayers on the basis of an arbitrary rank value C that is designated forthe corresponding downlink MIMO transmission through DRS pattern group#0 comprised of A (e.g., 12) REs (e.g., subcarriers acting as REs)specified in a time domain (e.g., on an OFDM symbol basis) and afrequency domain (e.g., on a subcarrier basis) and DRS pattern group #1comprised of B REs (e.g., 12 REs). Although numbers A and B of RS REsfor each DRS pattern group are basically identical to each other toprovide uniform channel estimation performance, the numbers A and B mayalso be different from each other on the basis of the importance of aspecific DRS pattern group or a DRS resource or layer.

The mapping or multiplexing scheme of DRS resources of the layer (or RSport) according to the present invention is based on the scheme designin which RS resources (RS patterns) mapped to individual layers areunchanged in response to an arbitrary rank value. In order to provide anRS pattern that is capable of being applied to Single User MIMO(SU-MIMO), Multi User MIMO (MU-MIMO), and DL CoMP, the RS position andpattern for each layer should be unchanged. The above-mentioned conceptmay be represented by ‘rank-independent one-to-one layer—to—RS resourcemapping’. In addition, according to the aforementioned distinctivemapping targets, the above-mentioned concept may also be represented by‘rank-independent one-to-one RS port—to—RS resource mapping’.

To accomplish this, for an arbitrary transmission rank value (Z), Z RSresources (or Z RS patterns) may be selected in a fixed order accordingto available rank values, from among RS resources (RS patterns) mappedto each transmission layer defined by the layer index described in thepresent invention. For example, provided that a transmission rank valueis set to ‘Z’, RS resources (patterns) for Z layer indexes may besequentially applied from Layer index #0 to Layer index #(Z−1).

FDM or CDM may be used as a basic method for multiplexing one or morelayer RS resources (patterns) on A or B RS REs of each DRS patterngroup. If necessary, TDM may be further used according to the detailsdesign result of each DRS pattern. Needless to say, detailedmultiplexing schemes, each of which is a combination of two or moreschemes from among the above-mentioned multiplexing schemes may also becontained in the proposal of the present invention.

A method for multiplexing D RS REs according to individual DRS patterngroups on the assumption that the sum of A RS REs and B RE REs for eachDRS pattern group is set to D is based on a method for multiplexingphysical resource REs to be discriminated among TDM, FDM or FDM/TDM. Ifnecessary, CDM may be used to multiplex RS physical resources among DRSpatter groups.

Under the condition that each DRS pattern group #0 or #1 includes A(e.g., 12) REs or B (e.g., 12) REs, a detailed description of theexemplary case in which RS patterns of layers formed according to anarbitrary rank value are CDM-processed in REs of the selected DRSpattern group will hereinafter be described in detail.

Code resources, that are capable of being applied to define individualDRS resources (patterns) for RS REs of an arbitrary DRS pattern groupaccording to the CDM, may include Orthogonal Variable Spreading Factor(OVSF) code, Discrete Fourier Transform (DFT)-based code, a Walsh- orWalsh-Hadamard-based orthogonal code sequence. In addition, such coderesources may include cyclic shifts of a CAZAC-based Generalized ChirpLike (GCL) sequence, Computer Generated CAZAC (CG-CAZAC) or Zadoff-Chu(ZC), and Zadoff-Chu zero correlation zone (ZC-ZCZ) sequence. Inaddition, the code resources may include cyclic shifts of aquasi-orthogonal-based cold code sequence, and Kasami sequence,m-sequence binaries. Such code resources may be one-dimensionallyapplied only to a time domain or a frequency domain in association withRS REs of each DRS pattern group, and may also be two-dimensionallyapplied to both of the time domain and the frequency domain. Such coderesources may be used as cover sequences in a time domain and/orfrequency domain in association with RS REs of each DRS pattern group.

In case of applying the above-mentioned arbitrary code sequence to eachDRS pattern group or all the DRS pattern groups, the arbitrary codesequence may be applied to REs of a frequency domain of an OFDM symbolincluding the corresponding RS RE, or may also be mapped to RS REs ofall the RS REs (on one or more DRS pattern groups).

FIGS. 5 and 6 illustrate the examples for multiplexing DRS resourcesmapped to a DRS pattern group using the CDM scheme according to oneembodiment of the present invention. FIG. 5 shows the exemplary case inwhich a cover sequence is used on a slot basis. For this purpose, acover sequence of the length 2 may be used (as denoted by a solid line).Application of the cover sequence of the length 2 for each slot may beinterpreted as application of the cover sequence of the length 4 interms of a subframe (as denoted by a dotted line). For example, assumingthat [1 −1] is applied to each of slot 0 and slot 1, [1 −1 1 −1] may beinterpreted as being applied to the subframe. FIG. 6 shows the exemplarycase in which the cover sequence is used in units of a subframe. Inorder to implement the example of FIG. 6, the separately-defined coversequence of the length 4 may be used as necessary. Tables 3 and 4illustrate exemplary cases where the cover sequence of the length 2 andthe cover sequence of the length 4 may be applied to DRS pattern groupG0 and DRS pattern group G1, respectively.

TABLE 3 Slot 0 Slot 1 l = 5 l = 6 l = 5 l = 6 k = 11 w0*G0 w1*G0 w0⁺*G0w1⁺*G0 k = 10 w0*G1 w1*G1 w0⁺*G1 w1⁺*G1 k = 6 w0*G0 w1*G0 w0⁺*G0 w1⁺*G0k = 5 w0*G1 w1*G1 w0⁺*G1 w1⁺*G1 k = 1 w0*G0 w1*G0 w0⁺*G0 w1⁺*G0 k = 0w0*G1 w1*G1 w0⁺*G1 w1⁺*G1

TABLE 4 Slot 0 Slot 1 l = 5 l = 6 l = 5 l = 6 k = 11 w0*G0 w1*G0 w2*G0w3*G0 k = 10 w0*G1 w1*G1 w2*G1 w3*G1 k = 6 w0*G0 w1*G0 w2*G0 w3*G0 k = 5w0*G1 w1*G1 w2*G1 w3*G1 k = l w0*G0 w1*G0 w2*G0 w3*G0 k = 0 w0*G1 w1*G1w2*G1 w3*G1

In Tables 3 and 4, l, k, slot, G0 and G1 are identical to those ofTables 1 and 2, and w0, w1, w2 and w3 may indicate individual elementsof the cover sequence. [w0 w1] and [w0+ w1+] may indicate a coversequence applied to Slot 0 and a cover sequence applied to Slot 1,respectively. [w0 w1] and [w0+ w1+] may be selected independently fromthe set of the cover sequence having the length of 2.

From among the orthogonal cover indexes of DRS resources (patterns)defined as CDM of the arbitrary DRS pattern group, some indexes may bedefined as an orthogonal cover sequence of the slot unit length 2, andsome other indexes may be defined as an orthogonal cover sequence of thesubframe unit length 4. Table 5 exemplarily shows the orthogonal coversequence of the length 4 and the orthogonal cover sequence of the length2.

TABLE 5 Orthogonal cover sequence Sequence index Length 4: [w0 w1 w2 w3]Length 2: [w0 w1] 0 [+l +l +l +l] [+l +l] 1 [+l −l +l −l] [+l −l] 2 [+l+l −l −l] — 3 [+l −l −l +l] — 4 [+j +j +j +j] [+j +j] 5 [+j −j +j −j][+j −j] 6 [+j +j −j −j] — 7 [+j −j −j +j] —

In Table 5, the sequence index may correspond to the code resourceindex. However, provided that the cover sequence (i.e., the coversequence of the length 2) is applied on a slot basis, the code resourceindex may be independently assigned to each slot and may be assigned toa combination of sequence indexes applied to Slot 0 and Slot 1. Forexample, one code resource index may be defined for a combination of [w0w1] and [w0+ w1+]) shown in Table 3.

Table 5 is disclosed only for illustrative purposes, and orthogonal coderesources of cyclic shifts of a CAZAC-based GCL (Generalized Chirp Like)sequence and CG-CAZAC or Zadoff-Chu sequence. In addition, cyclic shiftsof quasi-orthogonal-based gold code sequence, Kasami sequence, andm-sequence binaries may be used as code resources for covering.

Although not shown in FIGS. 5 and 6, scrambling may be applied to theDRS pattern group in the frequency or time-frequency domain, in additionto apply a cover sequence of a time domain to the DRS pattern.Scrambling may be applied to a DRS pattern group on an OFDM symbolbasis, or may also be applied to all the RS REs pertaining to the DRSpattern group. The scrambling may be UE-specifically,UE-group-specifically, or cell-specifically applied. Orthogonal VariableSpreading Factor (OVSF) code, Discrete Fourier Transform (DFT)-basedcode, Walsh- or Walsh-Hadamard-based orthogonal code sequences may beused as scrambling code sequences. In addition, cyclic shifts (CSs) ofCAZAC-based GCL sequence, CG-CAZAC, Zadoff-Chu (ZC) sequence, andZadoff-Chu zero correlation zone (ZC-ZCZ) may be used as scrambling codesequences. In addition, cyclic shifts (CSs) of quasi-orthogonal-basedgold code sequence or Kasami sequence, and m-sequence (binary) may alsobe used as scrambling code sequences. Code sequences for such scramblingare not defined as code resources for discriminating orthogonal DRSresources of the arbitrary DRS pattern group based on the CDM schemeaccording to usage purposes. That is, the code sequence fordiscriminating CDM code resources and the scrambling code sequence maybe individual defined and applied.

FIG. 7 exemplarily shows the physical channel structure for DRStransmission according to one embodiment of the present invention.

Referring to FIG. 7, each slot includes a symbol for data transmissionand a symbol (G0/G1) for DRS. In G0/G1 symbols, frequency resourcesmapped to DRS pattern group #0 (G0) and frequency resources mapped toDRS pattern group #1 (G1) may be multiplexed according to the FDM schemeas shown in FIG. 4. In the embodiment, it is possible to use anothermethod different from the resource mapping method of an orthogonal codesequence constructing an orthogonal DRS resource (pattern) in theCDM-based DRS pattern group. The length of a code sequence, that isapplied to RS REs of the arbitrary DRS pattern group so as to define theCDM-based orthogonal DRS resource (pattern), may be defined to beidentical to the number of RS REs contained in the corresponding DRSpattern group. For example, if the number of REs of a DRS pattern groupis set to 12, the length of a sequence for each RS may be set to 12 inresponse to 12 REs of the DRS pattern group. In this case, the sequencefor the RS may be mapped to all the RS REs contained in the DRS patterngroup. On the other hand, the length of a sequence for the RS may beidentical to the number of RS REs contained in each OFDM symbol of theDRS pattern group. In this case, one RS sequence may be mapped only toRS RE contained in the OFDM symbol, and the same RS sequence may berepeatedly mapped to OFDM symbols of the DRS pattern group.

In each DRS pattern group, several DRS resources (patterns) may beCDM-processed in a time domain and/or a frequency domain. For example,the CDM scheme may be implemented using a (quasi)-orthogonal code (i.e.,a cover sequence) for time spread. Code resources for CDM may includeorthogonal codes (for example, OVSF code, Walsh code, Walsh-Hadamardcode, and DFT code). Code resources for CDM may include cyclic shifts ofCAZAC GCL sequence, CG-CAZAC sequence, ZC sequence, and ZC-ZCZ. Inaddition, code resources for CDM may include cyclic shifts (CSs) ofquasi-orthogonal-based gold code sequence, Kasami sequence, andm-sequence binaries. The cover sequence multiplied by an RS sequence maybe applied on a slot basis or a subframe basis. If the cover sequence isapplied on a slot basis, the cover sequence (w0, w1) of the length 2 maybe used as shown in FIG. 7( a). If the cover sequence is applied on asubframe basis, the cover sequence (w0, w1, w2, w3) of the length 4 maybe used as shown in FIG. 7( b). If DRS is not precoded, RS sequence ismultiplied by a cover sequence in a time domain, and is then mapped tophysical resources for each physical antenna. On the other hand, if theDRS is precoded (i.e., layer RS), the cover sequence is multiplied byDRS REs in a time domain, and the DRS REs may be mapped to physicalresources for each physical antenna through precoding.

FIG. 8 shows exemplary allocation of DRS resources (patterns) accordingto one embodiment of the present invention. DRS resources according tothe present invention may be specified by an index pair including a DRSpattern group and a code resource index. For convenience of description,the present embodiment assumes the precoded DRS (i.e., layer RS). If DRSis not precoded, layer index shown in FIG. 8 may be replaced with anobject (e.g., a physical antenna port) corresponding to the physicalantenna. The scope or spirit of the present invention is not limitedthereto, and it should be noted that a layer index may be replaced witha virtual antenna port, a virtual antenna port index, an RS port, or anRS port index, differently from the above-mentioned layer indexdescribed above. For convenience of description, the embodiment of thepresent invention will be disclosed to cover all the above-mentionedcases for describing the case of a layer index.

Referring to FIG. 8, resources (e.g., DRS pattern group index and coderesource index) for layer RS on a DRS to which precoding is applied maybe determined using a layer index and associated parameters (e.g.,(virtual) antenna port index, antenna port, or RS port). For example,layer index or layer RS index may be mapped to layer RS resources. Inanother example, layer or layer RS index may be mapped to a (virtual)antenna port, and the (virtual) antenna port may be mapped to layer RSresources. The layer RS index may represent a logical index indicatingthe order of RSs defined per layer according to the proposal of thepresent invention, and may correspond to a layer index. The index of the(virtual) antenna port is an index indicating a logical order of eithera system defined in the present invention or a transmission mode. If theindex of the (virtual) antenna port for another conventionaltransmission mode is predetermined, a predetermined offset may beapplied to index configuration. Considering the sequential mapping ofthe layer index to the antenna RS port, the mapping between the layer RSand the layer RS resources may be defined to have the same order orformat as in the mapping between the antenna RS port and the RSresource. On the other hand, provided that permutation (or reordering)is applied to layer index, layer RS index, and antenna RS port, themapping order between the RS for each layer and layer RS resources maybe changed. In addition, when mapping between the RS for each layer andthe layer RS resource, additional parameters (e.g., UE-specificparameter) may be used (for example, as a cyclic offset).

Although not shown in FIG. 8, when scrambling is additionally applied tothe layer RS, a scrambling code resource (index) may be further definedas a layer RS resource. The scrambling code resource (index) may beUE-specifically, UE group-specifically, and cell-specifically defined.

If an arbitrary rank value is given, a DRS pattern group index firstmapping scheme, a code resource index first mapping scheme, or a hybridthereof may be used to map individual layers or (virtual) antenna portsto a DRS pattern. The DRS pattern group index first mapping schemesequentially maps individual layers or (virtual) antenna ports to DRSpattern group #0 and DRS pattern group #1. If the number of layers or(virtual) antenna ports to be mapped to the DRS pattern groups isinsufficient, code resources may be changed in the DRS pattern group.For example, the code resource first mapping scheme may firstly mapindividual layers or (virtual) antenna ports to DRS patterns of the DRSpattern group #0. If the number of layers or (virtual) antenna ports tobe mapped to the DRS patterns is insufficient, code resources are mappedto DRS patterns of the DRS pattern group #1. In addition, a hybrid ofthe DRS pattern group index first mapping scheme and the code resourceindex first mapping scheme may be used according to the rank value.

A method for mapping a layer, a layer RS, a virtual antenna port, avirtual antenna port index, an RS port or an RS port index to DRSresources will hereinafter be described with reference to Tables.According to the proposal of the present invention, DRS pattern groupsof individual layers are fixed and established irrespective of the rankvalue. For convenience of description, the following tables exemplarilyshow the layer index mapped to DRS resources. The following tables aredisclosed only for illustrative purposes, the scope or spirit of thepresent invention is not limited thereto, a layer or a layer index maybe converted into a layer RS, a layer RS index, a virtual antenna port,a virtual antenna port index, an RS port or an antenna port index. Inmore detail, although Tables shown in the present embodiment exemplarilydisclose the mapping relationship of resources defined as a DRS patterngroup and code of the layer, the scope or spirit of the presentinvention is not limited thereto, and can also be applied to the mappingrelationship of resources defined as a DRS pattern group and code indexof the virtual antenna port or RS port, instead of the layer. Forexample, after layer (or layer RS) may be mapped to DRS resources or anantenna RS port, the antenna RS port may be mapped to the DRS resources.In this case, reordering or permutation may be applied to layer index(layer RS index) and/or the antenna RS port. For example, although layerindexes of the following table is arranged in the order of‘0→1→2→3→4→5→6→7’, the layer indexes after execution of the reorderingmay be rearranged in the order of 0→3→5→7→1→2→4→6. Although thefollowing table exemplarily shows a plurality of ranks up to Rank 8 forconvenience of description, the scheme proposed by the present inventionmay also be equally or similarly extended even to the system having ahigher rank value.

In the following example, the number of REs of each DRS pattern groupmay be set to 12, and the length of a code sequence for RS may also beset to 12. In addition, according to a first method (Method 1), a totalof 8 code resources may be defined in different ways according toindividual DRS pattern groups. According to a second method (Method 2),a total of 4 code resources (that is, the same code resource for eachDRS pattern group may be established) may be defined. In addition, allof the code resource index #0 may be composed of ‘1’. In more detail, nocode may be applied to the case where one layer RS pattern isestablished in an arbitrary DRS pattern group.

TABLE 6 Layer DRS pattern Code resource Code resource index group indexindex (opt. 1) index (opt. 2) [Proposal #1.1-A] 0 0 0 0 1 0 1 1 2 1 2 03 1 3 1 4 0 4 2 5 0 5 3 6 1 6 2 7 1 7 3 [Proposal #1.1-B] 0 0 0 0 1 0 11 2 1 2 0 3 1 3 1 4 1 4 2 5 1 5 3 6 0 6 2 7 0 7 3

Proposal 1.1-A exemplarily shows the case where the DRS pattern group ischanged whenever the layer index is increased by 2. That is, if thelayer index is set to 0˜1, only the DRS pattern group #0 is used, andtwo code resource indexes are used for insufficient resources.Similarly, if the layer index is set to any one of 2˜3, 4˜5 and 6˜7,individual DRS pattern groups #1, #0 and #1 are sequentially applied.

Proposal 1.1-B exemplarily shows modification of the proposal 1.1-A.Proposal 1.1-B may also be interpreted as the case where the layer indexis rearranged in the proposal 1.1-A. In more detail, Method 2 of theproposal 1.1-B may correspond to the case where the layer indexes 4, 5,6 and 7 of Method 2 of the proposal 1.1-A are rearranged in the order of6→7→4→5.

TABLE 7 Layer DRS pattern Code resource Code resource index group indexindex (opt. 1) index (opt. 2) [Proposal #1.1-C] 0 0 0 0 1 1 1 0 2 0 2 13 1 3 1 4 0 4 2 5 1 5 2 6 0 6 3 7 1 7 3 [Proposal #1.1-D] 0 0 0 0 1 1 10 2 1 2 1 3 0 3 1 4 1 4 2 5 0 5 2 6 1 6 3 7 0 7 3

Proposal 1.1-C exemplarily shows the DRS pattern group index firstmapping scheme. That is, according to the proposal 1.1-C, layer indexesare sequentially mapped to DRS pattern group #0 and DRS pattern group#1. And, if the number of layer indexes is insufficient, code resourcesare changed in the DRS pattern group.

Proposal 1.1-D exemplarily shows modification of Proposal 1.1-C. In moredetail, Proposal 1.1-D exemplarily shows the exemplary usage of adifferent-format layer (or antenna port)—to—RS resource mapping schemeon the basis of a boundary between layer index 1 and layer index 2.

Proposal 1.1-C and Proposal 1.1-D may also be applied to the case where24 REs may be applied to the DRS pattern group in case of Rank 2 orhigher.

TABLE 8 Layer DRS pattern Code resource Code resource index group indexindex (opt. 1) index (opt. 2) [Proposal #1.1-E] 0 0 0 0 1 0 1 1 2 1 2 03 1 3 1 4 0 4 2 5 1 5 3 6 0 6 2 7 1 7 3 [Proposal #1.1-F] 0 0 0 0 1 0 11 2 1 2 0 3 1 3 1 4 1 4 2 5 0 5 3 6 1 6 2 7 0 7 3

Proposals 1.1-E and 1.1-F exemplarily show more uniform distributionmethods on higher layer RS indexes as compared to Proposals 1.1-A/1.1-B.

TABLE 9 Layer DRS pattern Code resource Code resource index group indexindex (opt. 1) index (opt. 2) [Proposal #1.1-G] 0 0 0 0 1 0 1 1 2 1 2 03 1 3 1 4 0 4 2 5 1 5 2 6 0 6 3 7 1 7 3 [Proposal #1.1-H] 0 0 0 0 1 0 11 2 1 2 0 3 1 3 1 4 1 4 2 5 0 5 2 6 1 6 3 7 0 7 3

Proposals 1.1-G and 1.1-H exemplarily show other methods of more uniformdistribution methods on higher layer RS indexes as compared to Proposals1.1-A/1.1-B.

According to Proposals 1.1-G and 1.1-H, when mapping or multiplexing ofDRS resources of layer (or RS port), RS resources (patterns) mapped toindividual layers according to an arbitrary rank value may be unchangedas necessary. Irrespective of a rank value, a DRS pattern group for eachlayer is fixed. For example, the present embodiment may provide therank-independent one-to-one layer-to-RS resource mapping scheme or therank-independent one-to-one RS port-to-RS resource mapping scheme.Because RS position and patterns for individual layers are unchanged,the rank-independent RS resource mapping scheme may provide RS patternscapable of being applied to SU-MIMO (Single User MIMO), MU-MIMO (MultiUser MIMO) or DL CoMP.

In addition, although the above-mentioned tables have disclosed themapping relationship of resources defined as a DRS pattern group andcode of the layer, the scope or spirit of the present invention is notlimited thereto, and it should be noted that the present embodiment canalso be applied to a variety of proposals of the mapping relationship ofresources defined as a DRS pattern group and code index of a virtualantenna port or RS port, instead of the layer. That is, the layer andlayer index mentioned in the above-mentioned tables may be convertedinto a virtual antenna port or RS port, and the virtual antenna portindex or RS port index as necessary.

TABLE 10 Layer DRS pattern Code resource Code resource index group indexindex (opt. 1) index (opt. 2) [Proposal #1.1-I] 0 0 0 0 1 0 1 1 2 0 2 23 0 3 3 4 1 4 0 5 1 5 1 6 1 6 2 7 1 7 3 [Proposal #1.1-J] 0 0 0 0 1 0 11 2 0 2 2 3 0 3 3 4 0 4 4 5 0 5 5 6 1 6 0 7 1 7 1

Proposals 1.1-I and 1.1-J exemplarily show a multiplexing scheme forlimiting physical resource overhead in a time-frequency resource regionfor time-frequency DM-RS transmission under any rank below either Rank-4or Rank-6.

In case of Proposal 1.1-J, the number of orthogonal code covers betweentransmission symbols of a time domain is not enough to generate 6 coderesources with time-frequency resources of one DRS pattern group in therange extending Rank-6, and a code resource having the correspondinglength in association with all or some parts of RS physical resources ofthe corresponding DRS pattern group may be defined as a CAZAC sequence,a DFT sequence, a ZC sequence, a GCL (general chirp-like) sequence or aWalsh sequence.

TABLE 11 Layer DRS pattern Code resource Code resource index group indexindex (opt. 1) index (opt. 2) [Proposal #1.1-K] 0 0 0 0 1 0 1 1 2 1 2 03 1 3 1 4 1 4 2 5 1 5 3 6 1 6 4 7 1 7 5 [Proposal #1.1-L] 0 0 0 0 1 1 10 2 0 2 1 3 1 3 1 4 1 4 2 5 1 5 3 6 1 6 4 7 1 7 5

Proposal 1.1-K and 1.1-L exemplarily show a method for limiting layerinterference in an RS of a lower layer index.

In case of the Proposals 1.1-K and 1.1-L, DRS pattern group #1 provides6 layer RS patterns. The number of orthogonal code covers betweentransmission symbols of a time domain is not enough to generate 6 coderesources with time-frequency resources of one DRS pattern group in therange extending Rank-6, a code resource having the corresponding lengthin association with all or some parts of RS physical resources of thecorresponding DRS pattern group may be defined as a CAZAC sequence, aDFT sequence, a ZC sequence, a GCL (general chirp-like) sequence or aWalsh sequence.

Next, under the condition that DRS pattern group #0 and DRS patterngroup #1 are comprised of A REs (e.g., 12 REs) and B REs (e.g., 12 REs),respectively, detailed proposals for the case where REs of a DRS patterngroup in which an RS pattern of layers formed in response to anarbitrary rank value is selected are multiplexed according to FDM, TDMor FDM/TDM scheme will hereinafter be described.

According to Proposals of the present invention, a DRS pattern group foreach layer is established irrespective of the rank value. Although thepresent embodiment exemplarily shows a layer index mapped to a DRSresource for convenience of description, the scope or spirit of thepresent invention is not limited thereto. In the following tables, thelayer index may be replaced with a layer RS index or an antenna RS port.In more detail, after the layer (or layer RS) may be mapped to a DRSresource or the layer (or layer RS) may be mapped to an antenna RS port,the antenna RS port may be mapped to the DRS resource. In this case,reordering or permutation may be applied to the layer index (layer RSindex) and/or the antenna RS port. For convenience of description,although the following table exemplarily shows a plurality of ranks upto Rank 8, proposals of the present invention may be equally orsimilarly extended even to a higher rank system.

In case of defining orthogonal code resources on REs used for individualDRS patterns, the proposals of the present invention may conceptuallycover that all REs are distinctively defined in different formats, forexample, subcarrier division form, symbol division form, orfrequency/symbol division form. Each division RE may be identified by anRS resource index.

The number of all REs of each DRS pattern group may be set to 12. RSresource indexes for each DRS pattern group generated in REs (i.e., 12REs) are considered to be different RE patterns of individual DRSpattern groups, such that the RS resource indexes may be defined asdifferent indexes (Method 1), or may be defined as the same indexbetween the same patterns (Method 2).

TABLE 12 Layer DRS pattern RS pattern RS pattern index group index index(opt. 1) index (opt. 2) [Proposal #1.2-A] 0 0 0 0 1 0 1 1 2 1 2 0 3 1 31 4 0 4 2 5 0 5 3 6 1 6 2 7 1 7 3 [Proposal #1.2-B] 0 0 0 0 1 0 1 1 2 12 0 3 1 3 1 4 1 4 2 5 1 5 3 6 0 6 2 7 0 7 3

Proposal 1.2-A exemplarily shows the case where a DRS pattern group ischanged whenever the layer index is increased by 2. That is, if thelayer index is set to 0˜1, only the DRS pattern group #0 is used, andtwo RS pattern indexes are used for insufficient resources. Similarly,if the layer index is set to any of 2˜3, 3˜4 and 6˜7, DRS pattern group#1, DRS pattern group #0, and DRS pattern group #1 are sequentiallyapplied to the layer index.

Proposal 1.2-B exemplarily shows modification of Proposal 1.2-A.Proposal 1.2-B may also be interpreted as the case where the layer indexis rearranged in the proposal 1.2-A. In more detail, Method 2 of theproposal 1.2-B may correspond to the case where the layer indexes 4, 5,6 and 7 are rearranged in the order of 6→7→4→5 in Method 2 of Proposal1.2-A.

TABLE 13 Layer DRS pattern RS pattern RS pattern index group index index(opt. 1) index (opt. 2) [Proposal #1.2-C] 0 0 0 0 1 1 1 0 2 0 2 1 3 1 31 4 0 4 2 5 1 5 2 6 0 6 3 7 1 7 3 [Proposal #1.2-D] 0 0 0 0 1 1 1 0 2 12 1 3 0 3 1 4 1 4 2 5 0 5 2 6 1 6 3 7 0 7 3

Proposal 1.2-C exemplarily shows the DRS pattern group index firstmapping scheme. That is, according to the proposal 1.2-C, layer indexesare sequentially mapped to DRS pattern group #0 and DRS pattern group#1. If the number of layer indexes is insufficient, an RS pattern indexis changed in the DRS pattern group. Proposal 1.2-D exemplarily showsmodification of the proposal 1.2-C. Proposals 1.2-C and 1.2-D can alsobe applied to the case where 24 REs are used in a DRS pattern group incase of Rank 2 or higher.

TABLE 14 Layer DRS pattern RS pattern RS pattern index group index index(opt. 1) index (opt. 2) [Proposal #1.2-E] 0 0 0 0 1 0 1 1 2 1 2 0 3 1 31 4 0 4 2 5 1 5 3 6 0 6 2 7 1 7 3 [Proposal #1.2-F] 0 0 0 0 1 0 1 1 2 12 0 3 1 3 1 4 1 4 2 5 0 5 3 6 1 6 2 7 0 7 3

Proposals 1.2-E and 1.2-F exemplarily show more uniform distributionmethods on higher layer RS indexes as compared to Proposals 1.2-A/1.2-B.

Next, under the condition that DRS pattern group #0 and DRS patterngroup #1 are comprised of A REs (e.g., 12 REs) and B REs (e.g., 12 REs),respectively, detailed proposals for the case where REs of thecorresponding DRS pattern group in which an RS pattern of layers formedin response to an arbitrary rank value is selected are multiplexedaccording to FDM, TDM or FDM/TDM scheme will hereinafter be described.

In case of defining orthogonal code resources on REs used for individualDRS patterns, the proposals of the present invention may conceptuallycover that all REs are distinctively defined in different formats, forexample, subcarrier division form, symbol division form, orfrequency/symbol division form. Each division RE may be identified by anRS resource index. In this case, as many REs as the maximum number oflayer indexes to be multiplexed from among all the REs of the arbitraryDRS pattern group may be divided as in the proposal #1.2, but it shouldbe noted that a smaller number of REs than the above-mentioned number ofREs may be divided in consideration of additional CDM multiplexing.

When defining orthogonal code resources on REs used for individual DRSpatterns, not only Walsh code or Walsh-Hadamard orthogonal codesequences on REs of a frequency domain, but also Walsh covering for REson OFDM symbols may be used. Orthogonal code resource allocation ofcyclic shifts on CAZAC-based GCL or ZC sequence may be applied to thepresent embodiment. In addition, cyclic shifts of quasi-orthogonal goldcode sequence, Kasami sequence or m-sequence binaries may be used ascode resources. In addition, when applying the above-mentioned arbitrarycode sequence to each DRS pattern group or the entire DRS pattern group,the arbitrary code sequence may be applied to REs of a frequency domainon an OFDM symbol having the corresponding RE, or may be mapped to allof the corresponding REs (on one or more DRS pattern groups).Differently from the above-mentioned description, the present embodimentmay generate/map sequences in response to some REs divided in FDM, TDMor FDM/TDM scheme of all the REs of the arbitrary DRS pattern group.When applying the resource allocation of the present invention, eachcode resource is defined as a code resource index.

Mapping individual layers to arbitrary RS patterns and/or code resourcesmay be achieved in a time-first scheme, a frequency first scheme, or acode-first scheme. If the above-mentioned mapping is achieved in threeresource regions using the multiplexing scheme, the mapping may beachieved in the order of time→frequency→code (i.e.,time-frequency-code), the order of time→code→frequency (i.e.,time-code-frequency), the order of frequency→time→code (i.e.,frequency-time-code), the order of frequency→code→time (i.e.,frequency-code-time), the order of code→time→frequency (i.e.,code-time-frequency), or the order of code→frequency→time (i.e.,code-frequency-time).

A method for mapping the layer to a DRS resource with reference toTables will hereinafter be described in detail. According to theproposals of the present invention, DRS pattern groups of individuallayers are established irrespective of a rank value. For convenience ofdescription, the layer index may be replaced with a layer RS index or anantenna RS port in the following tables. In other words, after layer (orlayer RS) may be mapped to DRS resources or an antenna RS port, theantenna RS port may be mapped to the DRS resources. In this case,reordering or permutation may be applied to layer index (layer RS index)and/or the antenna RS port. Although the following table exemplarilyshows a plurality of ranks up to Rank 8 for convenience of description,the scheme proposed by the present invention may also be equally orsimilarly extended even to the system having a higher rank value.

In the following tables, Method 1 and Method 2 may be used. According toMethod 1, the number of REs of each DRS pattern group may be set to 12,and RS pattern indexes generated in 12 REs are considered to bedifferent RE patterns of individual DRS pattern groups, such that the RSpattern indexes may be defined as different indexes. According to Method2, RS pattern indexes generated in 12 REs may be defined as the same REpatterns, such that they can be defined as the same index between thesame patterns.

In the following tables, the number of REs of each DRS pattern group maybe set to 12, and the length of a code sequence may be defined as 12.Differently from the above-mentioned setting, the present embodiment maygenerate/map sequences in response to some REs divided in FDM, TDM orFDM/TDM scheme of all the REs of the arbitrary DRS pattern group.According to Method (a), arbitrary numbers of code resources may bedifferently assigned to respective DRS pattern groups. In this case, thearbitrary code resources may be requested on an arbitrary DRS patterngroup, or as many code resources as the number of available coderesources may be defined. According to Method (b), the same coderesource setting for each DRS pattern group may be defined. In thiscase, the same code resource setting may be requested on a pattern groupor as many code resources as the number of available code resources maybe defined. Each code resource index #0 may be comprised of ‘1’. Thatis, if the layer RS pattern is assigned to a DRS pattern group, anorthogonal code may not be used as necessary.

TABLE 15 RS pattern RS pattern index & Code index & Code Layer DRSpattern resource index resource index index group index (opt. 1- b)(opt. 2- b) [Proposal #1.3-A] 0 0 0&0 0&0 1 0 0&1 0&1 2 1 1&0 0&0 3 11&1 0&1 4 0 2&0 1&0 5 0 2&1 1&1 6 1 3&0 1&0 7 1 3&1 1&1 [Proposal#1.3-B] 0 0 0&0 0&0 1 0 0&1 0&1 2 1 1&0 0&0 3 1 1&1 0&1 4 1 2&0 1&0 5 12&1 1&1 6 0 3&0 1&0 7 0 3&1 1&1

Proposal 1.3-A exemplarily shows the case where the DRS pattern group ischanged whenever the layer index is increased by 2. That is, if thelayer index is set to 0˜1 or 4˜5, only the DRS pattern group #0 is used,and two RS pattern indexes and/or two code resource indexes may be usedfor insufficient resources. Similarly, if the layer index is set to anyone of 2˜3 and 6˜7, only the DRS pattern group #1 is applied.

Proposal 1.3-B exemplarily shows modification of the proposal 1.3-A.Proposal 1.3-B may also be interpreted as the case where the layer indexis rearranged in the proposal 1.3-A. In more detail, Method 2-b of theproposal 1.3-B may correspond to the case where the layer indexes 4, 5,6 and 7 in Method 2-B of the proposal 1.3-A are rearranged in the orderof 6→7→4→5.

TABLE 16 RS pattern RS pattern index & Code index & Code Layer DRSpattern resource index resource index index group index (opt. 1- a)(opt. 2- a) [Proposal #1.3-C] 0 0 0&0 0&0 1 0 0&1 0&1 2 1 1&2 0&2 3 11&3 0&3 4 0 2&4 1&4 5 0 2&5 1&5 6 1 3&6 1&6 7 1 3&7 1&7 [Proposal#1.3-D] 0 0 0&0 0&0 1 0 0&1 0&1 2 1 1&2 0&2 3 1 1&3 0&3 4 1 2&4 1&4 5 12&5 1&5 6 0 3&6 1&6 7 0 3&7 1&7

TABLE 17 RS pattern RS pattern index & Code index & Code Layer DRSpattern resource index resource index index group index (opt. 1- b)(opt. 2- b) [Proposal #1.3-E] 0 0 0&0 0&0 1 0 0&1 0&1 2 1 1&0 0&0 3 11&1 0&1 4 0 2&2 1&2 5 0 2&3 1&3 6 1 3&2 1&2 7 1 3&3 1&3 [Proposal#1.3-F] 0 0 0&0 0&0 1 0 0&1 0&1 2 1 1&0 0&0 3 1 1&1 0&1 4 1 2&2 1&2 5 12&3 1&3 6 0 3&2 1&2 7 0 3&3 1&3

TABLE 18 RS pattern RS pattern index & Code index & Code Layer DRSpattern resource index resource index index group index (opt. 1- b)(opt. 2- b) [Proposal #1.3-G] 0 0 0&0 0&0 1 1 0&0 0&0 2 0 0&1 0&1 3 10&1 0&1 4 0 1&2 1&0 5 1 1&2 1&0 6 0 1&3 1&1 7 1 1&3 1&1 [Proposal#1.3-H] 0 0 0&0 0&0 1 1 0&0 0&0 2 1 0&1 0&1 3 0 0&1 0&1 4 1 1&2 1&0 5 01&2 1&0 6 1 1&3 1&1 7 0 1&3 1&1

Under the condition that each DRS pattern group #0 or #1 includes A(e.g., 12) REs or B (e.g., 12) REs, a detailed description of theexemplary case in which RS patterns of layers formed according to anarbitrary rank value are two-dimensionally CDM-processed in REs of thecorresponding DRS pattern group will hereinafter be described in detail.In more detail, in association with REs of the DRS pattern group, afirst code resource may be applied to a time domain, and a second coderesource may be applied to a frequency domain. The order of a timedomain and a frequency domain, each of which receives code resources,may be changed as necessary. For example, in association with REs of theDRS pattern group, a first code resource may be used as a cover sequencein a time domain, and a second code resource may be used as a scramblingcode resource in a frequency domain, or vice versa. In the meantime, itmay be possible to perform forward or reversal code index mapping inassociation with the order of OFDM symbol indexes. The forward orreversal code index mapping may be considered in the mapping processwhere each symbol having an element ‘1’ is not punctured to preventpattern orthogonality from being broken even in the puncturingsituation.

Code resources used for REs of each DRS pattern may include OVSF(Orthogonal Variable Spreading Factor) code, DFT (Discrete FourierTransform)-based code, and a Walsh or Walsh-Hadamard-based orthogonalcode sequence. In addition, code resources may include cyclic shifts ofa CAZAC-based GCL (Generalized Chirp Like) sequence, a CG-CAZAC(Computer Generated CAZAC) sequence, and a ZC or ZC-ZCZ (Zadoff-Chu zerocorrelation zone) sequence. In addition, code resources may includecyclic shifts of a quasi-orthogonal gold code sequence, a Kasamisequence, and m-sequence binaries.

Although the scope or spirit of the present invention is not limitedthereto, a first code resource for 2-D CDM includes an orthogonalsequence cover (e.g., Walsh cover) applied to a time domain. Forexample, the Walsh cover may include {1,1} or {1, −1} applied to REpairs of two contiguous OFDM symbols in the same pattern group. If threeOFDM symbols are contiguous to each other in the DRS pattern group, aDFT-based Walsh cover having the length of 3 may be used. In this case,two of three Walsh covers each having the length of 3 may be used. Inaddition, a second code resource for 2-D CDM may include a cyclic shiftsequence applied to REs contained in one OFDM symbol in the same DRSpattern group. For example, the second code resource may include cyclicshifts of CAZAC, ZC, ZCZ, gold code, Kasami sequences and m-sequencebinary.

A method for mapping layer or (virtual) antenna port to DRS resourceswill hereinafter be described in detail with reference to Tables.According to Proposals of the present invention, a DRS pattern group foreach layer is established irrespective of the rank value. Forconvenience of description, although the following table exemplarilyshows the layer index mapped to DRS resources, the scope or spirit ofthe present invention is not limited thereto. In the following tables,the layer index may be replaced with a layer RS index or an antenna RSport. In more detail, after the layer (or layer RS) may be mapped to aDRS resource or the layer (or layer RS) may be mapped to an antenna RSport, the antenna RS port may be mapped to the DRS resource. In thiscase, reordering or permutation may be applied to the layer index (layerRS index) and/or the antenna RS port. For convenience of description,although the following table exemplarily shows a plurality of ranks upto Rank 8, proposals of the present invention may be equally orsimilarly extended even to a higher rank system.

Layer RS patterns of the proposals #2.1 to #2.25 to be described belowshow resource multiplexing schemes of individual layer RSs extending toRank-8. If an arbitrary rank value is given, the proposals #2.1 to #2.25may be understood as the multiplexing pattern extending to layer RSindexes derived from the corresponding rank value. In other words,irrespective of the rank value, the same layer RS pattern, namely, thesame layer RS mapping, may be applied to the present embodiment.

In the following tables, the order of a DRS pattern group, a Walsh cover(WC) index, and a cyclic shift (CS) index may be described only fordistinction for convenience of description. Such index order may beapplied to an actual physical RE (or physical RE pattern) resource and acode resource index without change, or may be arbitrarily mappedthereto.

One or more patterns from among multiplexing patterns of all the layerREs described in arbitrary proposals from among one or more proposals ofthe following proposals #2.1˜#2.25 are combined such that the entirelayer RS patterns may be reconstructed. All the proposals capable ofbeing derived from the above-mentioned process may be contained inproposals of the present invention.

RS resources exemplarily shown in the proposals #2.1˜#2.25 are asfollows.

WC (Wash cover) index #0, #1 (for example, WC #0: {1,1}, WC #1: {1, −1})

CS (Cyclic Shift) index #0, #1

DRS pattern group index #0, #1

Case A exemplarily shows that WC is first mapped and CS is then mapped.

Case A exemplarily shows that CS is first mapped, and WC is then mapped.

Although the scope or spirit of the present invention is not limitedthereto, as can be seen from the following tables, WC index may be usedas a cover sequence resource and CS index may be used as a scramblingcode resource, or vice versa.

TABLE 19 Code resource Code resource Layer DRS pattern index (WC index(CS index group index index) index) [Proposal #2.1-A] 0 0 0 0 1 0 1 0 21 0 0 3 1 1 0 4 0 0 1 5 0 1 1 6 1 0 1 7 1 1 1 [Proposal #2.1-B] 0 0 0 01 0 0 1 2 1 0 0 3 1 0 1 4 0 1 0 5 0 1 1 6 1 1 0 7 1 1 1

Proposal 2.1-A exemplarily shows the case where RS resources are mappedin the order of WC index→DRS pattern group index→CS index in response tothe increasing layer index.

Proposal 2.1-B exemplarily shows the case where RS resources are mappedin the order of CS index→DRS pattern group index→WC index in response tothe increasing layer index.

TABLE 20 Code resource Code resource Layer DRS pattern index (WC index(CS index group index index) index) [Proposal #2.2-A] 0 0 0 0 1 0 1 0 21 0 0 3 1 1 0 4 1 0 1 5 1 1 1 6 0 0 1 7 0 1 1 [Proposal #2.2-B] 0 0 0 01 0 0 1 2 1 0 0 3 1 0 1 4 1 1 0 5 1 1 1 6 0 1 0 7 0 1 1

Proposal 2.2-A exemplarily shows modification of Proposal 2.1-A.Proposal 2.2-A may also be interpreted as the case where the layer indexis rearranged in the proposal 2.1-A. In more detail, the proposal 2.1-Amay correspond to the case where the layer indexes 4, 5, 6 and 7 arerearranged in the order of 6→7→4→5 in Proposal 2.1-A.

Proposal 2.2-B exemplarily shows modification of Proposal 2.1-B.Proposal 2.2-B may also be interpreted as the case where the layer indexis rearranged in the proposal 2.1-B. In more detail, the proposal 2.1-Bmay correspond to the case where the layer indexes 4, 5, 6 and 7 arerearranged in the order of 6→7→4→5 in Proposal 2.1-B.

TABLE 21 Code resource Code resource Layer DRS pattern index (WC index(CS index group index index) index) [Proposal #2.3-A] 0 0 0 0 1 0 1 0 20 0 1 3 0 1 1 4 1 0 0 5 1 1 0 6 1 0 1 7 1 1 1 [Proposal #2.3-B] 0 0 0 01 0 0 1 2 0 1 0 3 0 1 1 4 1 0 0 5 1 0 1 6 1 1 0 7 1 1 1

Proposal 2.3-A exemplarily shows the case where RS resources are mappedin the order of WC index→CS index→DRS pattern group index in response tothe increasing layer index.

Proposal 2.3-B exemplarily shows the case where RS resources are mappedin the order of CS index→WC index→DRS pattern group index in response tothe increasing layer index.

TABLE 22 Code resource Code resource Layer DRS pattern index (CS index(WC index group index index) index) [Proposal #2.4] 0 0 0 0 1 0 1 0 2 10 0 3 1 1 0 4 0 2 0 5 0 3 0 6 1 2 0 7 1 3 0 [Proposal #2.5] 0 0 0 0 1 01 0 2 1 0 0 3 1 1 0 4 1 2 0 5 1 3 0 6 0 2 0 7 0 3 0

Proposal 2.4 shows an exemplary model in which four cyclic shift (CS)code resources are used in the proposal 2.1 (i.e., no WC-based codemultiplexing).

Proposal 2.5 shows an exemplary model in which four cyclic shift (CS)code resources are used in the proposal 2.2 (i.e., no WC-based codemultiplexing).

TABLE 23 Code resource Code resource Layer DRS pattern index (CS index(WC index group index index) index) [Proposal #2.6] 0 0 0 0 1 0 1 0 2 10 0 3 1 1 0 4 0 2 0 5 0 3 0 6 1 2 1 7 1 3 1 [Proposal #2.7] 0 0 0 0 1 01 0 2 1 0 0 3 1 1 0 4 0 2 1 5 0 3 1 6 1 2 1 7 1 3 1

Proposal 2.6 shows an exemplary model in which four cyclic shift (CS)code resources are used in the proposal 2.1 (i.e., multiplexing of 2WC-based codes).

Proposal 2.7 shows an exemplary model in which four cyclic shift (CS)code resources are used in the proposal 2.1 (i.e., multiplexing of 2WC-based codes).

TABLE 24 Code resource Code resource Layer DRS pattern index (CS index(WC index group index index) index) [Proposal #2.8] 0 0 0 0 1 0 1 0 2 10 0 3 1 1 0 4 1 2 0 5 1 3 0 6 0 2 1 7 0 3 1 [Proposal #2.9] 0 0 0 0 1 01 0 2 1 0 0 3 1 1 0 4 1 2 1 5 1 3 1 6 0 2 1 7 0 3 1

Proposal 2.8 shows an exemplary case in which four CS code resources areused in the proposal 2.2 (i.e., multiplexing of 2 WC-based codes).

Proposal 2.9 shows an exemplary case in which four CS code resources areused in the proposal 2.2 (i.e., multiplexing of 2 WC-based codes).

TABLE 25 Code resource Code resource Layer DRS pattern index (CS index(WC index group index index) index) [Proposal #2.10] 0 0 0 0 1 0 0 1 2 10 0 3 1 0 1 4 0 0 2 5 0 1 2 6 1 0 2 7 1 1 2 [Proposal #2.11] 0 0 0 0 1 00 1 2 1 0 0 3 1 0 1 4 1 0 2 5 1 1 2 6 0 0 2 7 0 1 2

Proposal 2.10 shows an exemplary case in which three Walsh covers (WCs)and two CS code resources are used in the proposal 2.1.

Proposal 2.11 shows an exemplary case in which three Walsh covers (WCs)and two CS code resources are used in the proposal 2.2.

TABLE 26 Code resource Code resource Layer DRS pattern index (CS index(WC index group index index) index) [Proposal #2.12] 0 0 0 0 1 0 1 0 2 10 0 3 1 1 0 4 1 0 1 5 1 1 1 6 1 2 0 7 1 3 0 [Proposal #2.13] 0 0 0 0 1 01 0 2 1 0 0 3 1 1 0 4 1 0 1 5 1 1 1 6 1 2 1 7 1 3 1

Proposal 2.12 shows an exemplary model in which uneven layer RS patternmapping to the DRS pattern group, four cyclic shift (CS) code resources,and two WC code resources are used.

Proposal 2.13 shows an exemplary model in which uneven layer RS patternmapping to the DRS pattern group, four CS code resources and two WC coderesources are used (Compared to Proposal 2.12, different WCs may be usedin the layer-6 or layer-7 RS patterns.

TABLE 27 Code resource Code resource Layer DRS pattern index (CS index(WC index group index index) index) [Proposal #2.14] 0 0 0 0 1 0 0 1 2 10 0 3 1 0 1 4 1 1 0 5 1 1 1 6 1 1 2 7 1 1 2 [Proposal #2.15] 0 0 0 0 1 00 1 2 1 0 0 3 1 0 1 4 1 1 0 5 1 1 1 6 1 0 2 7 1 0 2

Proposal 2.14 exemplarily shows uneven layer RS pattern mapping to theDRS pattern group, three Walsh covers (WCs) and two CS code resourcesare used.

Proposal 2.15 exemplarily shows uneven layer RS pattern mapping to thepattern group, three Walsh covers (WCs) and two CS code resources areused (Compared to the proposal 2.14, different CSs may be used in thelayer-6 and layer-7 RS patterns).

TABLE 28 Code resource Code resource Layer DRS pattern index (CS index(WC index group index index) index) [Proposal #2.16] 0 0 0 0 1 0 1 0 2 10 0 3 1 1 0 4 1 0 1 5 1 1 1 6 1 0 2 7 1 1 2 [Proposal #2.17] 0 0 0 0 1 00 1 2 1 0 0 3 1 1 0 4 1 0 1 5 1 1 1 6 1 0 2 7 1 1 2

Proposal 2.16 shows an exemplary model in which uneven layer RS patternmapping to the DRS pattern group, three Walsh covers (WCs) and twocyclic shift (CS) code resources are used.

Proposal 2.17 shows an exemplary model in which uneven layer RS patternmapping to the DRS pattern group, three WCs and two CS code resourcesare used. The proposal 2.17 uses different cyclic shifts at Layer 0 andone RS pattern as compared to the proposal 2.14.

TABLE 29 Code resource Code resource Layer DRS pattern index (CS index(WC index group index index) index) [Proposal #2.18] 0 0 0 0 1 0 1 0 2 10 0 3 1 0 1 4 1 1 0 5 1 1 1 6 1 1 2 7 1 1 2 [Proposal #2.19] 0 0 0 0 1 01 0 2 1 0 0 3 1 0 1 4 1 1 0 5 1 1 1 6 1 0 2 7 1 0 2

Proposal 2.18 shows an exemplary model in which uneven layer RS patternmapping to the DRS pattern group, three Walsh covers (WCs) and twocyclic shift (CS) code resources are used.

Proposal 2.19 shows an exemplary model in which uneven layer RS patternmapping to the DRS pattern group, three WCs and two CS code resourcesare used. The proposal 2.19 uses different CSs at Layer 6 and 7 RSpatterns as compared to the proposal 2.18.

TABLE 30 Code resource Code resource Layer DRS pattern index (WC index(CS index group index index) index) [Proposal #2.1-C] 0 0 0 0 1 0 1 0 21 0 0 3 1 1 0 4 0 0 1 5 1 0 1 6 0 1 1 7 1 1 1 [Proposal #2.1-D] 0 0 0 01 0 0 1 2 1 0 0 3 1 0 1 4 0 1 0 5 1 1 0 6 0 1 1 7 1 1 1

Proposals 2.1-C and 2.1-D exemplarily show a method for more uniformlyarranging DRS patterns in the DRS pattern group at a high layer RS indexas compared to the proposals 2.1-A and 2.1-B.

TABLE 31 Code resource Code resource Layer DRS pattern index (WC index(CS index group index index) index) [Proposal #2.2-C] 0 0 0 0 1 0 1 0 21 0 0 3 1 1 0 4 1 0 1 5 0 0 1 6 1 1 1 7 0 1 1 [Proposal #2.2-D] 0 0 0 01 0 0 1 2 1 0 0 3 1 0 1 4 1 1 0 5 0 1 0 6 1 1 1 7 0 1 1

Proposals 2.2-C and 2.2-D exemplarily show a method for more uniformlyarranging DRS patterns in the DRS pattern group at a high layer RS indexas compared to the proposals 2.2-A and 2.2-B.

TABLE 32 Code resource Code resource Layer DRS pattern index (WC index(CS index group index index) index) [Proposal #2.2-E] 0 0 0 0 1 0 0 0 21 1 0 3 1 1 0 4 0 2 0 5 1 2 0 6 0 3 0 7 1 3 0 [Proposal #2.2-F] 0 0 0 01 0 0 0 2 1 1 0 3 1 1 0 4 1 2 0 5 0 2 0 6 1 3 0 7 0 3 0

Proposals 2.2-E and 2.2-F exemplarily show a method for more uniformlyarranging DRS patterns in the DRS patter group at a high layer RS indexas compared to the proposals 2.2-A and 2.2-B.

TABLE 33 Code resource Code resource Layer DRS pattern index (WC index(CS index group index index) index) [Proposal #2.2-G] 0 0 0 0 1 0 0 0 21 1 1 3 1 1 1 4 0 2 0 5 1 2 1 6 0 3 0 7 1 3 1 [Proposal #2.2-H] 0 0 0 01 0 0 0 2 1 1 1 3 1 1 1 4 1 2 1 5 0 2 0 6 1 3 1 7 0 3 0

Proposals 2.2-G and 2.2-H exemplarily show a method for more uniformlyarranging DRS patterns in the DRS pattern group at a high layer RS indexas compared to the proposals 2.2-A and 2.2-B.

TABLE 34 Code resource Code resource Layer DRS pattern index (WC index(CS index group index index) index) [Proposal #2.2-I] 0 0 0 0 1 0 0 0 21 1 1 3 1 1 1 4 0 2 2 5 1 2 2 6 0 3 3 7 1 3 3 [Proposal #2.2-J] 0 0 0 01 0 0 0 2 1 1 1 3 1 1 1 4 1 2 2 5 0 2 2 6 1 3 3 7 0 3 3

Proposals 2.2-I and 2.2-J exemplarily show a method for more uniformlyarranging DRS patterns in the DRS pattern group at a high layer RS indexas compared to the proposals 2.2-A and 2.2-B.

TABLE 35 Code resource Code resource Layer DRS pattern index (CS index(WC index group index index) index) [Proposal #2.4-A] 0 0 0 0 1 0 1 0 21 0 0 3 1 1 0 4 0 2 0 5 1 2 0 6 0 3 0 7 1 3 0 [Proposal #2.5-A] 0 0 0 01 0 1 0 2 1 0 0 3 1 1 0 4 1 2 0 5 0 2 0 6 1 3 0 7 0 3 0

Proposals 2.4-A and 2.5-A exemplarily show a method for more uniformlyarranging DRS patterns in the DRS pattern group at a high layer RS indexas compared to the proposals 2.4 and 2.5.

TABLE 36 Code resource Code resource Layer DRS pattern index (CS index(WC index group index index) index) [Proposal #2.6-A] 0 0 0 0 1 0 1 0 21 0 0 3 1 1 0 4 0 2 0 5 1 2 1 6 0 3 0 7 1 3 1 [Proposal #2.7-A] 0 0 0 01 0 1 0 2 1 0 0 3 1 1 0 4 0 2 1 5 1 2 1 6 0 3 1 7 1 3 1

Proposals 2.6-A and 2.7-A exemplarily show a method for more uniformlyarranging DRS patterns in the DRS pattern group at a high layer RS indexas compared to the proposals 2.6 and 2.7.

TABLE 37 Code resource Code resource Layer DRS pattern index (CS index(WC index group index index) index) [Proposal #2.8-A] 0 0 0 0 1 0 1 0 21 0 0 3 1 1 0 4 1 2 0 5 0 2 1 6 1 3 0 7 0 3 1 [Proposal #2.9-A] 0 0 0 01 0 1 0 2 1 0 0 3 1 1 0 4 1 2 1 5 0 2 1 6 1 3 1 7 0 3 1

Proposals 2.8-A and 2.9-A exemplarily show a method for more uniformlyarranging DRS patterns in the DRS pattern group at a high layer RS indexas compared to the proposals 2.8 and 2.9.

TABLE 38 Code resource Code resource Layer DRS pattern index (CS index(WC index group index index) index) [Proposal #2.10-A] 0 0 0 0 1 0 0 1 21 0 0 3 1 0 1 4 0 0 2 5 1 0 2 6 0 1 2 7 1 1 2 [Proposal #2.11-A] 0 0 0 01 0 0 1 2 1 0 0 3 1 0 1 4 1 0 2 5 0 0 2 6 1 1 2 7 0 1 2

Proposals 2.10-A and 2.11-A exemplarily show a method for more uniformlyarranging DRS patterns in the DRS pattern group at a high layer RS indexas compared to the proposals 2.10 and 2.11.

TABLE 39 Code resource Code resource Layer DRS pattern index (CS index(WC index group index index) index) [Proposal #2.20] 0 0 0 0 1 0 1 0 2 10 0 3 1 3 0 4 1 1 0 5 1 4 0 6 1 2 0 7 1 5 0 [Proposal #2.21] 0 0 0 0 1 01 0 2 1 0 0 3 1 1 0 4 1 2 0 5 1 0 1 6 1 1 1 7 1 2 1

Proposal 2.20 exemplarily shows a method for mapping an uneven layer RSpattern to the DRS pattern group. A detailed description thereof is asfollows.

DRS pattern group #0: 2 cyclic shifts (CSs); DRS pattern group #1: 6cyclic shifts (CSs)

Mapping of (cyclic shift, WC) to a layer index may be permuted inassociation with individual DRS pattern groups #0 and #1.

Proposal 21 exemplarily shows a method for mapping an uneven layer RSpattern to the DRS pattern group. A detailed description thereof is asfollows.

DRS pattern group #0: 2 cyclic shifts (CSs); DRS pattern group #1: 3cyclic shifts (CSs) and 2 WCs

Mapping of (cyclic shift, WC) to a layer index may be permuted inassociation with individual DRS pattern groups #0 and #1.

TABLE 40 Code resource Code resource Layer DRS pattern index (CS index(WC index group index index) index) [Proposal #2.22] 0 0 0 0 1 0 0 1 2 10 0 3 1 1 0 4 1 2 0 5 1 0 1 6 1 1 1 7 1 2 1 [Proposal #2.23] 0 0 0 0 1 00 1 2 1 0 0 3 1 1 0 4 1 2 0 5 1 3 0 6 1 4 0 7 1 5 0

Proposal 2.22 exemplarily shows a method for mapping an uneven layer RSpattern to the DRS pattern group. A detailed description thereof is asfollows.

DRS pattern group #0: 2 WCs; DRS pattern group #1: 2 WCs and 3 cyclicshifts (CSs)

Mapping of (cyclic shift, WC) to a layer index may be permuted inassociation with individual DRS pattern groups #0 and #1.

Proposal 2.23 exemplarily shows a method for mapping an uneven layer RSpattern to the DRS pattern group. A detailed description thereof is asfollows.

DRS pattern group #0: 2 WCs; DRS pattern group #1: 6 cyclic shifts (CSs)

Mapping of (cyclic shift, WC) to a layer index may be permuted inassociation with individual DRS pattern groups #0 and #1.

TABLE 41 Code resource Code resource Layer DRS pattern index (CS index(WC index group index index) index) [Proposal #2.24] 0 0 0 0 1 0 1 0 2 10 0 3 1 1 0 4 0 0 1 5 1 0 1 6 0 1 1 7 1 1 1 [Proposal #2.25] 0 0 0 1 0 22 1 0 3 1 2 4 0 1 5 1 1 6 0 3 7 1 3

Proposal 2.24 exemplarily shows a method for distributing an equal layerto the DRS pattern groups #0 and #1. A detailed description thereof isas follows.

DRS pattern groups #0 and #1: 2 cyclic shifts (CSs) and 2 WCs

Mapping of (group, cyclic shift, WC) to a layer index may be permuted inassociation with individual DRS pattern groups #0 and #1.

Proposal 25 exemplarily shows a method for distributing an equal layerto the DRS pattern groups #0 and #1. A detailed description thereof isas follows.

DRS pattern groups #0 and #1: 4 cyclic shifts (CSs) or four 4WCs

Mapping of (group, cyclic shift, WC) to a layer index may be permuted inassociation with individual DRS pattern groups #0 and #1.

The power boosting according to one embodiment of the present inventionwill hereinafter be described. If CDM multiplexing is applied to DRSpatterns proposed in the present invention, a beamforming gain isgradually reduced in proportion to higher rank transmission, and thenumber of layer RS that is CDM-processed in the same resources isincreased. Therefore, power boosting for providing channel estimationperformance appropriate for a high rank may be requested. In this case,if power (or power spectral density (PSD)) assigned to respective layersfor PDSCH data transmission is different from power (or PSD) of an RSphysical resource element (PRE) of the corresponding layer, a relativedifference or ratio among an absolute value of power (or PSD) of the RS,power (or PSD) of data PRE, and power (or PSD) established in a layer RSof the RS PRE may be transmitted through cell-specific or UE (orRN)-specific RRC signaling, or may be transmitted through L1/L2 PDCCHcontrol signaling. A detailed method for establishing power (or PDS)between PREs of an RS for each layer will hereinafter be described.Although the following proposals will disclose the operation forapplying power boosting to RS physical resources when applying power (orPSD) to physical resources, the scope or spirit of the present inventionis not limited thereto, and the present embodiment can also be appliedto the scheme for establishing/signaling the relationship of dataphysical resources and RS physical power (or PSD) under a generalsituation.

Method 1: Allocation of the Same Layer RS & Data Power (or PSD)

In order to provide even channel estimation performance for eachtransmission layer, the same power (or PSD) for RS per transmissionlayer may be established. Therefore, in response to the number of layerRS patterns CDM-processed in a specific DRS pattern group, a total ofpower (or PSD) established in PREs of the corresponding DRS patterngroup may be established in different ways according to DRS patterngroups. In addition, power boosting of the RS may be used in the presentembodiment. Power (or PSD) of overall PDSCH and RS transmissionresources and/or a transmission layer may be established and signaled,and a detailed description thereof is as follows.

Method 1: A difference or relative ratio between power (or PSD) of thedata transmission PRE of the entire subframe and power (or PSD) of theRS transmission PRE may be configured. Specifically, when power boostingis performed, a difference in absolute value or relative ratio betweenpower (or PSD) of a data transmission PRE and power (or PSD) of an RStransmission PRE in a transmission symbol to which RS is transmitted maybe configured, and a difference in absolute value or relative ratiobetween power (or PSD) of a data transmission PRE on a transmissionsymbol to which no RS is transmitted and power (or PSD) of the RStransmission PRE may be configured. In this case, the relationshipbetween power (or PSD) of the data transmission layer for eachtransmission layer and power (or PSD) of the corresponding layer RS maybe calculated on the assumption that the same power is established inindividual transmission layers. In this case, power (or PSD) betweendata and RS may be established in units of all PREs or each layer inconsideration of different signal superposition situations of respectivelayers in a data transmission PRE and an RS transmission PRE. Forexample, during Rank-5 transmission, in the data transmission PRE, fivetransmission layer information (or signal or energy) or an arbitrarynumber of transmission layer information (or signal or energy) accordingto the precoding codebook are coded and then superposed. In contrast, inthe RS PRE, the corresponding designated layer RS information (or signalor energy) is coded and superposed on the basis of the number of RSpatterns multiplexed in the DRS patter group to which the correspondingPRE pertains. If necessary, a scaling factor may also be reflected suchthat the resultant data is configured. Configuration for the above,information regarding a absolute difference in power (or PDS) per PRE orlayer between the configured data and RS, or information regarding adifference between the same in view of a relative ratio may betransmitted through cell-specific or UE (or RN)-specific RRC signaling,or may also be transmitted through L1/L2 PDCCH control signaling.

Method 2: Differently from Method 1, a difference or relative ratiobetween power (or PSD) of the data transmission layer of the entiresubframe and power (or PSD) of the RS transmission layer may beconfigured. Specifically, when power boosting is performed, a differencein absolute value or relative ratio between power (or PSD) of a datatransmission layer and power (or PSD) of an RS transmission layer in atransmission symbol to which RS is transmitted may be configured, and adifference in absolute value or relative ratio between power (or PSD) ofa data transmission layer on a transmission symbol to which no RS istransmitted and power (or PSD) of the RS transmission layer may beconfigured. In this case, power (or PSD) between data and RS may beestablished in units of all PREs or each layer in consideration ofsignal superposition of respective layers in a data transmission PRE andan RS transmission PRE. For example, during Rank-5 transmission, in thedata transmission PRE, five transmission layer information (or signal orenergy) parts or an arbitrary number of transmission layer information(or signal or energy) parts are coded according to the precodingcodebook, and then superposed. In contrast, in the RS PRE, thecorresponding designated layer RS information (or signal or energy) iscoded and superposed on the basis of the number of RS patternsmultiplexed in the DRS patter group to which the corresponding PREpertains. If necessary, the scaling factor may also be reflected in theabove-mentioned result. Information regarding a difference in absolutevalue of power of individual transmission layers between the configureddata and the RS or information regarding a difference in relative ratioof power between the data and the RS may be transmitted throughcell-specific or UE (or RN)-specific RRC signaling, or may also betransmitted through L1/L2 PDCCH control signaling.

Scheme 2: Allocation of Different Layer RS & Data Power (or PSD)

In order to assign a weight in view of a channel estimation performancefor each transmission layer and/or a decoding performance, differentpower values (or different PSD values) for RS may be assigned toindividual transmission layers. Therefore, according to the number oflayer RS patterns CDM-processed in a specific DRS pattern group, totalpower (or total PSD) to be established for PREs of the corresponding DRSpattern group may be differently established in individual DRS patterngroups. In addition, power boosting for RS (or DRS) may be used in thepresent embodiment. Power (or PSD) of overall PDSCH and RS transmissionresources and/or a transmission layer may be established and signaled,and a detailed description thereof is as follows.

Method 1: A difference or relative ratio between power (or PSD) of thedata transmission PRE of the entire subframe and power (or PSD) of theRS transmission PRE may be configured. Specifically, when power boostingis performed, a difference in absolute value or relative ratio betweenpower (or PSD) of a data transmission PRE and power (or PSD) of an RStransmission PRE in a transmission symbol to which RS is transmitted maybe configured, and a difference in absolute value or relative ratiobetween power (or PSD) of a data transmission PRE on a transmissionsymbol to which no RS is transmitted and power (or PSD) of the RStransmission PRE may be configured. In this case, the relationshipbetween power (or PSD) of the data transmission layer for eachtransmission layer and power (or PSD) of the corresponding layer RS maybe calculated on the assumption that different powers are assigned torespective transmission layers. In more detail, on the same assumptionas described above, information regarding a difference in absolute valueor relative ratio between powers of individual or specific layer typesmay be explicitly signaled, or the information regarding the differencemay also be differently assigned to respective transmission layersaccording to a specific rule in response to an implicitly-applied rankvalue in such a manner that different power assignment can beidentified. In this case, power (or PSD) between data and RS may beestablished in units of all PREs or each layer in consideration ofdifferent signal superposition situations of respective layers in a datatransmission PRE and an RS transmission PRE. For example, during Rank-5transmission, in the data transmission PRE, five transmission layerinformation (or signal or energy) parts or an arbitrary number oftransmission layer information (or signal or energy) parts are codedaccording to the precoding codebook and then superposed. In contrast, inthe RS PRE, the corresponding designated layer RS information (or signalor energy) is coded and superposed on the basis of the number of RSpatterns multiplexed in the DRS patter group to which the correspondingPRE pertains. If necessary, the scaling factor may also be reflectedsuch that the resultant data is configured. Information regarding adifference in absolute value of power (or PDS) among the configureddata, RS PRE and transmission layer or information regarding adifference in relative ratio among the same may be transmitted throughcell-specific or UE (or RN)-specific RRC signaling, or may also betransmitted through L1/L2 PDCCH control signaling. Needless to say, ifpower (or PSD) set values of RS and/or data differently established inunits of a group of a transmission layer or in units of each layer, orindirect indication information associated with the power set values areexplicitly signaled, this information may be transmitted throughcell-specific signaling, UE (or RN)-specific RRC signaling or L1/L2PDCCH control signaling.

Method 2: A difference or relative ratio between power (or PSD) of thedata transmission layer of the entire subframe and power (or PSD) of theRS transmission layer may be configured. Specifically, when powerboosting is performed, a difference in absolute value or relative ratiobetween power (or PSD) of a data transmission layer and power (or PSD)of an RS transmission layer in a transmission symbol to which RS istransmitted may be configured, and a difference in absolute value orrelative ratio between power (or PSD) of a data transmission layer on atransmission symbol to which no RS is transmitted and power (or PSD) ofthe RS transmission layer may be configured. In this case, therelationship between power (or PSD) of the data transmission layer foreach transmission layer and power (or PSD) of the corresponding layer RSmay be calculated on the assumption that different powers are assignedto respective transmission layers. In more detail, on the sameassumption as described above, information regarding a difference inabsolute value or relative ratio between powers of individual orspecific layer types may be explicitly signaled, or the informationregarding the difference may also be differently assigned to respectivetransmission layers according to a specific rule in response to animplicitly-applied rank value in such a manner that different powerassignment can be identified. In this case, power (or PSD) between dataand RS may be established in units of all PREs or each layer inconsideration of different signal superposition situations of respectivelayers in a data transmission PRE and an RS transmission PRE. Forexample, during Rank-5 transmission, in the data transmission PRE, fivetransmission layer information (or signal or energy) parts or anarbitrary number of transmission layer information (or signal or energy)parts are coded according to the precoding codebook and then superposed.In contrast, in the RS PRE, the corresponding designated layer RSinformation (or signal or energy) is coded and superposed on the basisof the number of RS patterns multiplexed in the DRS patter group towhich the corresponding PRE pertains. If necessary, the scaling factormay also be reflected such that the resultant data is configured.Information regarding a difference in absolute value of power (or PDS)among the configured data, RS PRE and transmission layer or informationregarding a difference in relative ratio among the same may betransmitted through cell-specific or UE (or RN)-specific RRC signaling,or may also be transmitted through L1/L2 PDCCH control signaling.Needless to say, if power (or PSD) set values of RS and/or datadifferently established in units of a group of a transmission layer orin units of each layer, or indirect indication information associatedwith the power set values are explicitly signaled, this information maybe transmitted through cell-specific signaling, UE (or RN)-specific RRCsignaling or L1/L2 PDCCH control signaling.

FIG. 9 is a block diagram illustrating a transmitter according to oneembodiment of the present invention. FIG. 9 shows exemplary downlinktransmission of the transmitter in a MIMO mode. In a MIMO system, a basestation (BS) may transmit one or more codewords via a downlink. Thecodeword may be mapped to a transmission block from a higher layer. FIG.9 assumes the exemplary case where two codewords are transmitted.

Referring to FIG. 9, the receiver includes a scrambling module 801, amodulation mapper 802, a layer mapper 803, a layer RS inserting module804, a precoder 805, a resource element mapper 806, and an OFDM signalgenerator 807. The layer RS inserting module 804 may also be implementedas a functional block of the layer mapper 803 as necessary. Thescrambling module 801 and the modulation mapper 802 are configured toprocess one or more codewords (CWs) to be complex symbols. Thereafter,the layer mapper 803 maps complex symbols of one or more codewords (CWs)to a plurality of layers. In this case, the number of layers isidentical to a rank value. The layer RS inserting module 804 inserts theinventive layer RS into a layer (or (virtual) antenna port). The layerRS is defined by a DRS pattern group and a code resource index. Ifnecessary, the layer RS may be defined by additional code resource indexfor 2-D CDM. In addition, the layer RS may also be defined usingscrambling code resources. The precoder 805 distributes/assigns thelayer to individual transmission antennas using a predeterminedprecoding matrix. The precoder 805 may be represented by a matrix of(Nt×v) (where Nt is the number of transmission antennas, and v is aspatial multiplexing rate). The precoder 805 may adaptively use theprecoding matrix according to a channel situation (e.g., a precodingmatrix indicator (PMI)). The set or aggregate of precoding matrixespredetermined by the transmitter/receiver is called a codebook. Theresource element mapper 806 maps the precoded complex sequence totime-frequency resource elements for the corresponding antenna. The OFDMsignal generator 807 generates an OFDM symbol by applying IFFT to eachcomplex symbol mapped to the time-frequency resource element. The OFDMsymbol is transmitted to each antenna through antenna ports.

FIGS. 10 to 14 exemplarily show the mapping relationship between acodeword and a layer according to one embodiment of the presentinvention. The codeword-to-layer mapping relationship may be equally orsimilarly applied even to the other case where the RS sequence is mappedto a layer. For convenience of description, FIGS. 10 to 14 exemplarilyshow the case where two codewords (CW1 and CW2) are mapped to a layer.However, under the condition of Nt transmission antennas, a maximum ofNt ranks may be used, and Nt codewords (CWs) may be independentlytransmitted. In FIGS. 10 to 14, each number input to the precoder mayindicate a layer index (or (virtual) antenna port).

FIGS. 10 and 11 exemplarily show the basic codeword-to-layer mappingrelationship. As can be seen from the codeword-to-layer mappingrelationship shown in FIGS. 10 and 11, the order of layer indexesrequires logical indexing in which layers to be added in response to theincreasing rank are sequentially arranged (ordered). FIG. 10 exemplarilyshows the case of Rank 1˜4 and FIG. 11 exemplarily shows the other caseof Rank 5˜8. Referring to FIGS. 10 and 11, if one codeword (CW) ismapped to one layer, the codeword (CW) may be directly input to theprecoder, or may be input to the precoder after passing through theserial/parallel (S/P) converter. In contrast, if one codeword (CW) ismapped to two or more layers, the codeword (CW) is mapped to two or morelayers through the S/P converter, such that the mapped result is theninput to the precoder. Function of the S/P converter may correspond tothe layer mapper 803 of FIG. 9. The layer RS inserting module 805 shownin FIG. 9 may be functionally located between the S/P converter and theprecoder. Table 42 numerically shows the codeword-to-layer mappingrelationship of FIGS. 10 and 11.

TABLE 42 Number of Number of Codeword-to-layer mapping, layers codewordsi = 0, 1, . . . , M^(layer) _(symb) − 1 1 1 x⁽⁰⁾(i) = d⁽⁰⁾(i) M^(layer)_(symb) = M⁽⁰⁾ _(symb) 2 2 x⁽⁰⁾(i) = d⁽⁰⁾(i) M^(layer) _(symb) = x⁽¹⁾(i)= d⁽¹⁾(i) M⁽⁰⁾ _(symb) = M⁽¹⁾ _(symb) 3 2 x⁽⁰⁾(i) = d⁽⁰⁾(i) M^(layer)_(symb) = x⁽¹⁾(i) = d⁽¹⁾(2i) M⁽⁰⁾ _(symb) = M⁽¹⁾ _(symb)/2 x⁽²⁾(i) =d⁽¹⁾(2i + 1) 4 2 x⁽⁰⁾(i) = d⁽⁰⁾(2i) M^(layer) _(symb) = x⁽¹⁾(i) =d⁽⁰⁾(2i + 1) M⁽⁰⁾ _(symb)/2 = M⁽¹⁾ _(symb)/2 x⁽²⁾(i) = d⁽¹⁾(2i) x⁽³⁾(i)= d⁽¹⁾(2i + 1) 5 2 x⁽⁰⁾(i) = d⁽⁰⁾(2i) M^(layer) _(symb) = x⁽¹⁾(i) =d⁽⁰⁾(2i + 1) M⁽⁰⁾ _(symb)/2 = M⁽¹⁾ _(symb)/3 x⁽²⁾(i) = d⁽¹⁾(3i) x⁽³⁾(i)= d⁽¹⁾(3i + 1) x⁽⁴⁾(i) = d⁽¹⁾(3i + 2) 6 2 x⁽⁰⁾(i) = d⁽⁰⁾(3i) M^(layer)_(symb) = x⁽¹⁾(i) = d⁽⁰⁾(3i + 1) M⁽⁰⁾ _(symb)/3 = M⁽¹⁾ _(symb)/3 x⁽²⁾(i)= d⁽⁰⁾(3i + 2) x⁽³⁾(i) = d⁽¹⁾(3i) x⁽⁴⁾(i) = d⁽¹⁾(3i + 1) x⁽⁵⁾(i) =d⁽¹⁾(3i + 2) 7 2 x⁽⁰⁾(i) = d⁽⁰⁾(3i) M^(layer) _(symb) = x⁽¹⁾(i) =d⁽⁰⁾(3i + 1) M⁽⁰⁾ _(symb)/3 = M⁽¹⁾ _(symb)/4 x⁽²⁾(i) = d⁽⁰⁾(3i + 2)x⁽³⁾(i) = d⁽¹⁾(4i) x⁽⁴⁾(i) = d⁽¹⁾(4i + 1) x⁽⁵⁾(i) = d⁽¹⁾(4i + 2) x⁽⁶⁾(i)= d⁽¹⁾(4i + 3) 8 2 x⁽⁰⁾(i) = d⁽⁰⁾(4i) M^(layer) _(symb) = x⁽¹⁾(i) =d⁽⁰⁾(4i + 1) M⁽⁰⁾ _(symb)/4 = M⁽¹⁾ _(symb)/4 x⁽²⁾(i) = d⁽⁰⁾(4i + 2)x⁽³⁾(i) = d⁽⁰⁾(4i + 3) x⁽⁴⁾(i) = d⁽¹⁾(4i) x⁽⁵⁾(i) = d⁽¹⁾(4i + 1) x⁽⁶⁾(i)= d⁽¹⁾(4i + 2) x⁽⁷⁾(i) = d⁽¹⁾(4i + 3)

In Table 42, x^((a))(i) is an i-th symbol of the layer ‘a’, andd^((n))(i) is an i-th symbol of a codeword ‘n’. M^(layer) _(symb) is thenumber of complex symbols mapped to the layer, and M^((n)) _(symb) isthe number of complex symbols contained in the codeword ‘n’.

FIG. 12 shows the extended codeword-to-layer mapping relationship. Theexample of FIG. 12 may be used either for one case where a buffercorresponding to an arbitrary codeword is empty or for a rank overridingcase. The case where the buffer corresponding to the codeword is emptymay include HARQ (hybrid automatic repeat and request) transmission.Basic items of FIG. 12 are identical to those of FIGS. 10 and 11. Table43 numerically shows the codeword-to-layer mapping relationship of FIG.12.

TABLE 43 Number of Number of Codeword-to-layer mapping, layers codewordsi = 0, 1, . . . , M_(symb) ^(layer) − 1 1 1 x⁽⁰⁾(i) = d⁽¹⁾(i) M_(symb)^(layer) = M_(symb) ⁽¹⁾ 2 1 x⁽⁰⁾(i) = d^((n))(2i) M_(symb) ^(layer) =M_(symb) ^((n))/2, x⁽¹⁾(i) = d^((n))(2i + 1) n = 1 or 2 3 1 x⁽⁰⁾(i) =d^((n))(3i) M_(symb) ^(layer) = M_(symb) ^((n))/3, x⁽¹⁾(i) =d^((n))(3i + 1) n = 1 or 2 x⁽²⁾(i) = d^((n))(3i + 2) 4 1 x⁽⁰⁾(i) =d^((n))(4i) M_(symb) ^(layer) = M_(symb) ^((n))/4, x⁽¹⁾(i) =d^((n))(4i + 1) n = 1 or 2 x⁽²⁾(i) = d^((n))(4i + 2) x⁽³⁾(i) =d^((n))(4i + 3)

In Table 43, x^((a))(i) is an i-th symbol of the layer ‘a’, andd^((n))(i) is an i-th symbol of the codeword ‘n’. M^(layer) _(symb) isthe number of complex symbols mapped to the layer, and M^((n)) _(symb)is the number of complex symbols contained in the codeword ‘n’.

FIGS. 13 and 14 exemplarily show the codeword-to-layer mappingrelationship in the case where the layer index is reordered. FIGS. 13and 14 exemplarily show the case in which a different format of layer-RSport mapping is applied on the basis of a boundary between Rank-2 andRank-3 without using the rank-independent layer—to—RS port mapping. Theabove-mentioned situation will hereinafter be described with referenceto Tables 44 and 45. Table 44 exemplarily shows the layer-to-RS portmapping (or layer-RS port mapping) scheme in case of Rank-1 and Rank-2.Table 45 exemplarily shows the layer-to-RS port mapping (or layer-RSport mapping) scheme in case of ranks from Rank-3 to Rank-8. Table 44shows some parts of the proposal #1.1-B, and Table 45 shows some partsof the proposal #1.1-D.

TABLE 44 Layer DRS pattern Code resource index group index index (opt.2) 0 0 0 1 0 1

TABLE 45 Layer DRS pattern Code resource index group index index (opt.2) 0 0 0 1 1 0 2 1 1 3 0 1 4 1 2 5 0 2 6 1 3 7 0 3

In Tables 44 and 45, the order of layer indexes may requires logicalindexing in which layers to be added in response to the increasing rankare sequentially arranged (ordered). If necessary, the order of thelayer indexes may be rearranged according to a specific purpose. FIGS.13 and 14 show the example of layer ordering.

Reordering of layer indexes may be carried out by a series ofpreprocessing modules, or may be understood as logical change of themapping relationship between the layer index and the (virtual) antennaport. For example, reordering of layer indexes may also be understood bya method for sequentially indexing newly added/defined layers inresponse to the increasing rank value when mapping the layer index ofFIG. 12 to the (virtual) antenna port. In this case, it may beunderstood that the layer RS resource is mapped on the basis of a layerindex or (virtual) antenna port. Basic items are identical to those ofFIGS. 10, 11, and 12.

FIG. 15 is a block diagram illustrating a receiver according to oneembodiment of the present invention. FIG. 15 shows a method for enablinga user equipment (UE) to receive signals from a base station (BS) undera MIMO mode.

Referring to FIG. 15, the receiver includes an antenna, a radiofrequency (RF) module block 1201, a CP remove block 1202, a Fast FourierTransform (FFT) block 1203, a channel estimator 1204, and a MIMOdecoding block 1205. The RF module block 1201 may amplify and filtereach downlink transmission signal that is input to M (where M≧1)physical reception antennas. The CP remove block 1202 removes a timesample part corresponding to a CP from the reception OFDM symbolinterval. The FFT block 1203 performs FFT on the CP-removed sample. Thechannel estimator 1204 may be connected to an output terminal of the FFTblock. From among a subcarrier signal sample region corresponding to thePRB-unit frequency resource region pre-scheduled through a PDCCH for DLchannel assignment, signals are detected/extracted from REs mapped to RS(e.g., demodulation reference signal (DM-RS)) in such a manner thatchannel estimation is performed. A transmitter of the base station (BS)may apply the same precoding as in data REs to DM-RS RE, and thecorresponding precoder is combined with an RF channel during the channelestimation process of the UE receiver such that it can form anequivalent channel coefficient. The MIMO decoding block 1205 constructsthe (N×M) channel matrix for data REs contained in a frequency resourcedomain on the basis of signals extracted from DM-RS REs using thechannel estimator 1204, performs MIMO decoding, and forms and outputs Nreception layers or N reception streams. Thereafter, the decodingprocess and channel decoding process may be applied to N receptionlayers or N reception streams during the UE reception process.

FIG. 16 is a block diagram illustrating a base station (BS) and a userequipment (UE) applicable to embodiments of the present invention.

Referring to FIG. 16, a wireless communication system includes a BS 110and a UE 120. In downlink, a transmitter may be a part of the BS 110,and a receiver may be a part of the UE 120. In uplink, a transmitter maybe a part of the UE 120, and a receiver may be a part of the BS 110. TheBS 110 includes a processor 112, a memory 114, and a radio frequency(RF) unit 116. The processor 112 may be constructed to implement theprocedures and/or methods disclosed in the embodiments of the presentinvention. The memory 114 may be connected to a processor 112, and storevarious information related to operations of the processor 112. The RFunit 116 is connected to the processor 112, and transmits and/orreceives RF signals. The UE 120 includes a processor 122, a memory 124,and an RF unit 126. The processor 122 may be constructed to implementthe procedures and/or methods disclosed in the embodiments of thepresent invention. The memory 124 may be connected to a processor 122,and store various information related to operations of the processor122. The RF unit 126 is connected to the processor 122, and transmitsand/or receives RF signals. The BS 110 and/or the UE 120 may include asingle antenna or multiple antennas.

The aforementioned embodiments are achieved by combination of structuralelements and features of the present invention in a predetermined type.Each of the structural elements or features should be consideredselectively unless specified separately. Each of the structural elementsor features may be carried out without being combined with otherstructural elements or features. Also, some structural elements and/orfeatures may be combined with one another to constitute the embodimentsof the present invention. The order of operations described in theembodiments of the present invention may be changed. Some structuralelements or features of one embodiment may be included in anotherembodiment, or may be replaced with corresponding structural elements orfeatures of another embodiment. Moreover, it will be apparent that someclaims referring to specific claims may be combined with another claimsreferring to the other claims other than the specific claims toconstitute the embodiment or add new claims by means of amendment afterthe application is filed.

The embodiments of the present invention have been described based onthe data transmission and reception between the base station and theuser equipment. A specific operation which has been described as beingperformed by the base station may be performed by an upper node of thebase station as the case may be. In other words, it will be apparentthat various operations performed for communication with the userequipment in the network which includes a plurality of network nodesalong with the base station can be performed by the base station ornetwork nodes other than the base station. The base station may bereplaced with terms such as a fixed station, Node B, eNode B (eNB), andaccess point. Also, the user equipment may be replaced with terms suchas mobile station (MS) and mobile subscriber station (MSS).

The embodiments according to the present invention can be implemented byvarious means, for example, hardware, firmware, software, or theircombination. If the embodiment according to the present invention isimplemented by hardware, the embodiment of the present invention can beimplemented by one or more application specific integrated circuits(ASICs), digital signal processors (DSPs), digital signal processingdevices (DSPDs), programmable logic devices (PLDs), field programmablegate arrays (FPGAs), processors, controllers, microcontrollers,microprocessors, etc.

If the embodiment according to the present invention is implemented byfirmware or software, the embodiment of the present invention may beimplemented by a type of a module, a procedure, or a function, whichperforms functions or operations described as above. Software code maybe stored in a memory unit and then may be driven by a processor. Thememory unit may be located inside or outside the processor to transmitand receive data to and from the processor through various means whichare well known.

It will be apparent to those skilled in the art that the presentinvention can be embodied in other specific forms without departing fromthe spirit and essential characteristics of the invention. Thus, theabove embodiments are to be considered in all respects as illustrativeand not restrictive. The scope of the invention should be determined byreasonable interpretation of the appended claims and all change whichcomes within the equivalent scope of the invention are included in thescope of the invention.

INDUSTRIAL APPLICABILITY

Exemplary embodiments of the present invention can be applied to awireless communication system. In more detail, the exemplary embodimentsof the present invention can be applied to a method and apparatus fortransmitting a reference signal (RS) using multiple antennas.

The invention claimed is:
 1. A method of mapping signals in a wirelesscommunication system, the method comprising: mapping first referencesignals for each antenna port of a first set of antenna ports to a firstgroup of resource elements in one or more resource blocks; and mappingsecond reference signals for each antenna port of a second set ofantenna ports to a second group of resource elements in the one or moreresource blocks, wherein orthogonal sequences are multiplied with thefirst reference signals or the second reference signals, and wherein thefirst set of antenna ports comprises antenna ports {N, N+1, N+4, N+6}and the second set of antenna ports comprises antenna ports {N+2, N+3,N+5, N+7}.
 2. The method of claim 1, wherein the first group of resourceelements or the second group of resource elements in one resource blockcomprise three pairs of resource elements, two resource elements in eachpair are contiguous in a time domain, and two neighboring pairs ofresource elements are separated by 5 subcarriers in a frequency domain.3. The method of claim 1, wherein the first group of resource elementsor the second group of resource elements shows a pattern as shown in theTable below: Even-numbered slot Odd-numbered slot l = M l = M + 1 l = Ml = M + 1 k = 11 G0 G0 G0 G0 k = 10 G1 G1 G1 G1 k = 6 G0 G0 G0 G0 k = 5G1 G1 G1 G1 k = 1 G0 G0 G0 G0 k = 0 G1 G1 G1 G1

where k represents a subcarrier index in a resource block, 1 representsan Orthogonal Frequency Division Multiplexing (OFDM) symbol index, Mrepresents an integer of 0 to 5, G0 represents the first group ofresource elements, and G1 represents the second group of resourceelements.
 4. The method of claim 1, wherein the orthogonal sequences aremultiplied with the first or second reference signals in units of two orfour neighboring resource elements with the same subcarrier index. 5.The method of claim 1, wherein the one or more resource blocks are usedfor a Physical Downlink Shared Channel (PDSCH).
 6. A method of receivingreference signals in a wireless communication system, the methodcomprising: receiving first reference signals for each antenna port of afirst set of antenna ports, wherein the first reference signals aremapped to a first group of resource elements in one or more resourceblocks; and receiving second reference signals for each antenna port ofa second set of antenna ports, wherein the second reference signals aremapped to a second group of resource elements in the one or moreresource blocks, wherein orthogonal sequences are multiplied with thefirst reference signals or the second reference signals, and wherein thefirst set of antenna ports comprises antenna ports {N, N+1, N+4, N+6}and the second set of antenna ports comprises antenna ports {N+2, N+3,N+5, N+7}.
 7. The method of claim 6, wherein the first group of resourceelements or the second group of resource elements in one resource blockcomprise three pairs of resource elements, two resource elements in eachpair are contiguous in a time domain, and two neighboring pairs ofresource elements are separated by 5 subcarriers in a frequency domain.8. The method of claim 6, wherein the first group of resource elementsor the second group of resource elements shows a pattern as shown in theTable below: Even-numbered slot Odd-numbered slot l = M l = M + 1 l = Ml = M + 1 k = 11 G0 G0 G0 G0 k = 10 G1 G1 G1 G1 k = 6 G0 G0 G0 G0 k = 5G1 G1 G1 G1 k = 1 G0 G0 G0 G0 k = 0 G1 G1 G1 G1

where k represents a subcarrier index in a resource block, 1 representsan Orthogonal Frequency Division Multiplexing (OFDM) symbol index, Mrepresents an integer of 0 to 5, G0 represents the first group ofresource elements, and G1 represents the second group of resourceelements.
 9. The method of claim 6, wherein the orthogonal sequences aremultiplied with the first or second reference signals in units of two orfour neighboring resource elements with the same subcarrier index. 10.The method of claim 6, wherein the one or more resource blocks are usedfor a Physical Downlink Shared Channel (PDSCH).
 11. The method of claim10, further comprising: demodulating the PDSCH using the first or secondreference signals.
 12. A communication apparatus used in a wirelesscommunication system, the communication apparatus comprising: a RadioFrequency (RF) unit; and a processor, wherein the processor isconfigured to map first reference signals for each antenna port of afirst set of antenna ports to a first group of resource elements in oneor more resource blocks, and to map second reference signals for eachantenna port of a second set of antenna ports to a second group ofresource elements in the one or more resource blocks, wherein orthogonalsequences are multiplied with the first reference signals or secondreference signals, and wherein the first set of antenna ports comprisesantenna ports {N, N+1, N+4, N+6} and the second set of antenna portscomprises antenna ports {N+2, N+3, N+5, N+7}.
 13. The communicationapparatus of claim 12, wherein the first group of resource elements orthe second group of resource elements in one resource block comprisethree pairs of resource elements, two resource elements in each pair arecontiguous in a time domain, and two neighboring pairs of resourceelements are separated by 5 subcarriers in a frequency domain.
 14. Thecommunication apparatus of claim 12, wherein the first group of resourceelements or the second group of resource elements shows a pattern asshown in the Table below: Even-numbered slot Odd-numbered slot l = M l =M + 1 l = M l = M + 1 k = 11 G0 G0 G0 G0 k = 10 G1 G1 G1 G1 k = 6 G0 G0G0 G0 k = 5 G1 G1 G1 G1 k = 1 G0 G0 G0 G0 k = 0 G1 G1 G1 G1

where k represents a subcarrier index in a resource block, 1 representsan Orthogonal Frequency Division Multiplexing (OFDM) symbol index, Mrepresents an integer of 0 to 5, G0 represents the first group ofresource elements, and G1 represents the second group of resourceelements.
 15. The communication apparatus of claim 12, wherein theorthogonal sequences are multiplied with the first or second referencesignals in units of two or four neighboring resource elements with thesame subcarrier index.
 16. The communication apparatus of claim 12,wherein the one or more resource blocks are used for a Physical DownlinkShared Channel (PDSCH).
 17. A communication apparatus used in a wirelesscommunication system, the communication apparatus comprising: a RadioFrequency (RF) unit; and a processor, wherein the processor isconfigured to receive first reference signals for each antenna port of afirst set of antenna ports, wherein the first reference signals aremapped to a first group of resource elements in one or more resourceblocks, and to receive second reference signals for each antenna port ofa second set of antenna ports, wherein the second reference signals aremapped to a second group of resource elements in the one or moreresource blocks, wherein orthogonal sequences are multiplied with thefirst reference signals or the second reference signals, and wherein thefirst set of antenna ports comprises antenna ports {N, N+1, N+4, N+6}and the second set of antenna ports comprises antenna ports {N+2, N+3,N+5, N+7}.
 18. The communication apparatus of claim 17, wherein thefirst group of resource elements or the second group of resourceelements in one resource block comprise three pairs of resourceelements, two resource elements in each pair are contiguous in a timedomain, and two neighboring pairs of resource elements are separated by5 subcarriers in a frequency domain.
 19. The communication apparatus ofclaim 17, wherein the first group of resource elements or the secondgroup of resource elements shows a pattern as shown in the Table below:Even-numbered slot Odd-numbered slot l = M l = M + 1 l = M l = M + 1 k =11 G0 G0 G0 G0 k = 10 G1 G1 G1 G1 k = 6 G0 G0 G0 G0 k = 5 G1 G1 G1 G1 k= 1 G0 G0 G0 G0 k = 0 G1 G1 G1 G1

where k represents a subcarrier index in a resource block, 1 representsan Orthogonal Frequency Division Multiplexing (OFDM) symbol index, Mrepresents an integer of 0 to 5, G0 represents the first group ofresource elements, and G1 represents the second group of resourceelements.
 20. The communication apparatus of claim 17, wherein theorthogonal sequences are multiplied with the first or second referencesignals in units of two or four neighboring resource elements with thesame subcarrier index.
 21. The communication apparatus of claim 17,wherein the one or more resource blocks are used for a Physical DownlinkShared Channel (PDSCH).
 22. The communication apparatus of claim 21,wherein the processor is further configured to demodulate the PDSCHusing the first or second reference signals.